Possibility of scroll list with fixed headers?

I gave you problem a hard think this afternoon during a long drive, and came up with a method that's not too bad. The normal entries in the list would be UIListButtons. The Headers would be UIListContainers with each having a UIListButton as a child. This would allow the code to move the header UIListButtons through their localPosition while leaving the parents in place. This solution does not require parallel graphics as I suggest you use above. Here is a lightly tested body of code that implements the idea. I'm sure there are improvements to be made, but it is a proof of concept. Note most of the code is setting up the list. The code that handles the header movement (or non-movement) is small.

 // Note:  This script must execute after EZGUI List movement code.
 //   Use Edit/Project Settings/Script Execution Order if you need it.
 
 using System;
 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class HeaderList : MonoBehaviour {
     public TextAsset ta;              // Text file with a sorted list of strings
     public UIScrollList uisl;         // Scroll list
     public GameObject goPrefabEntry;  // Prefab for an entry
     public GameObject goPrefabHeader; // Prefab for a header
     
     private Vector3 v3Header;         // Position of the header of the list
     
     private List<Transform> artrHeader = new List<Transform>();
     
     private int iCurr = 0;             // Index of the current header being used.
     private float fHeight;             // Height of a header
     
     void Start() {
         BuildList();
         
         uisl.clipContents = false;     // Doesn't work with clipping turned on
         v3Header   = uisl.transform.position;  // Figure the position of the header
         v3Header.y = v3Header.y + uisl.viewableArea.y / 2.0f - fHeight / 2.0f;
         v3Header.z -= 0.2f;        
     }
     
     // Builds all the headers and entries for the scroll list
     void BuildList() {
         
         Transform tr = new GameObject().transform;        // Insert a blank/dummy header in the 
         Transform trChild = new GameObject().transform;   //   beginning of the header list to 
         trChild.parent = tr;                              //   remove a boundry condition
         Vector3 v3 = Vector3.zero;
         v3.y = 10000;
         tr.position = v3;
         artrHeader.Add(trChild);
         
         // Parse the text file of sorted strings into a string array
         string[] arst = ta.text.Split(new char[] {'\r','\n'},StringSplitOptions.RemoveEmptyEntries);
         
         // Insert the top header
         char ch = 'A';
         InsertHeader (ch);
         
         // Process the sorted list of strings
         for (int i = 0; i < arst.Length; i++) {
             if (arst[i][0] != ch) {  // If the first letter changed, insert a new one header
                 ch = arst[i][0];
                 InsertHeader(ch);
             }
             
             // Insert a new entry.  
             GameObject go = Instantiate(goPrefabEntry) as GameObject;
             UIListButton uilb = go.GetComponent<UIListButton>();
             uilb.Text = arst[i];
             uilb.Data = arst[i];
             uilb.scriptWithMethodToInvoke = this;
             uilb.methodToInvoke = "DoClick";
             uisl.AddItem (go);
         }
         
         tr = new GameObject().transform;        // Insert a blank/dummy header at the 
         trChild = new GameObject().transform;   //   end of the header list to 
         trChild.parent = tr;                    //   remove a boundry condition
         v3 = Vector3.zero;
         v3.y = -10000;
         tr.position = v3;
         artrHeader.Add(trChild);
     }
     
     // Inserts a header into the list.  Note a header consists of an 
     //   empty game object witha UIListItemContainer component and the 
     //   actual UIListButton is a child of that object (with a 
     //     localPosition of (0,0,0).
     void InsertHeader(char ch) {
         GameObject goParent = new GameObject();
         goParent.AddComponent<UIListItemContainer>();
         GameObject go = Instantiate(goPrefabHeader) as GameObject;
         UIListButton uilb = go.GetComponent<UIListButton>();
         fHeight = uilb.height;
         uilb.Text = ch.ToString();
         go.transform.parent = goParent.transform;
         uisl.AddItem (goParent);
         artrHeader.Add (go.transform);
     }
       
     // This code needs to be executed last.  You may need to modify the 
     //   order of the script executions to make sure this executes last
     void LateUpdate() {
         
         // Put the header we modified last frame back in place
         artrHeader[iCurr].localPosition = Vector3.zero;  
         
         // Find the header we should use.  Note I rescan the 
         //   list because a fast swipe might go past more than one
         //   header in a frame.
         iCurr = 0;
         for (int i = 0;  i <= artrHeader.Count; i++) {
             if (artrHeader[i].parent.position.y < v3Header.y)
                 break;
             iCurr++;
         } 
         iCurr--;
         
         // Put the header that we should use in the header position.
         artrHeader[iCurr].localPosition = artrHeader[iCurr].InverseTransformPoint(v3Header);
     
         // If the next header is pushing the current header, adjust the current header's 
         //    position.
         if (artrHeader[iCurr+1].parent.position.y + fHeight >= v3Header.y) {
             Vector3 v3 = artrHeader[iCurr].localPosition;
             v3.y += (artrHeader[iCurr+1].parent.position.y + fHeight) - v3Header.y;
             artrHeader[iCurr].localPosition = v3;
             
         }
     }
     
     
     // Process a mouse click on an entry
     void DoClick() {
         string st = (string)uisl.LastClickedControl.Data;
         Debug.Log (st);
     }
 }