3D Textbox

Hi, I'm trying to create a 3D textbox for a educational vocabulary translationprogram.

The Problem is, that the TextMesh class is not really optimized for this kinda stuff.

My Problem is, that I don't have a Textmarker so the user can edit the center of the word too. I was thinking of manually implementing it with a '|' character, but that way the letters would shift around as you parse through the text which would look kinda awkward. Does anybody know a solution for this problem?

Currently I'm doing something like this:

 void Update()
 {
     if(ItsText.Length <= itsMaxCharacters)
     {
         foreach(char aChar in Input.inputString)
         {
             if(aChar == "\b"[0] && ItsText.Length > 0)
                 ItsText = ItsText.Substring(0, ItsText.Length-1);
             else if(aChar != "\n"[0])
             {
                 if(ItsText[ItsText.Length-1] == '|')
                 {
                     ItsText = ItsText.Substring(0, ItsText.Length-1);
                     ItsText += aChar + "|";
                 }
                 else
                     ItsText += aChar;
             }
         }
     }
 }

Using the guisystem is not an option because the text should rotate in 3D space and turn around