Using CustomPropertyDrawer in OnGUI of ScriptableWizard

I have a ScriptableWizard where I have overwritten the OnGUI entirely and that works nicely. I have a CustomPropertyDrawer for a non-MonoBehaviour class that works nicely with when invoked as a PropertyField (both from MonoBehaviours and the default OnGUI of a ScriptableWizard). I can also easily invoke the property drawer in custom editors of MonoBehaviours with:

 EditorGUILayout.PropertyField(serializedObject.FindProperty("inventoryType"));

But as ScriptableWizard doesn't seem to have a serializedObject, I don't get how I would manually invoke the PropertyField in my custom OnGUI of the ScriptableWizard. On the other hand, it's obviously possible, as it is done when I don't overwrite the OnGUI.

Here's minimal CustomPropertyDrawer for reference:

 using UnityEngine;
 using System.Collections;
 using UnityEditor;
 using System.Linq;
 using PointClick;
 
 [CustomPropertyDrawer(typeof(InventoryTypeRestriction))]
 public class InventoryTypeEditor : PropertyDrawer {

     static string[] tagNames = new string {"Potion", "Armor", "Key"};

     public override void OnGUI (Rect position, SerializedProperty property, GUIContent label)
     {
         EditorGUI.BeginProperty(position, label, property);
 
         position = EditorGUI.PrefixLabel(position, GUIUtility.GetControlID(FocusType.Passive), label);
 
         int indent = EditorGUI.indentLevel;
         EditorGUI.indentLevel = 0;
         SerializedProperty flags = property.FindPropertyRelative("flags");
         flags.intValue = EditorGUI.MaskField(position, flags.intValue, tagNames, EditorStyles.popup);
         EditorGUI.indentLevel = indent;
         EditorGUI.EndProperty();
     }
 }

And a minimal InventoryTypeRestriction would look as:

 [System.Serializable]
 class InventoryTypeRestriction {
 
     [HideInInspector]
     public int flags = 0;
 
 }

So the question is: How do I invoke a CustomPropertyDrawer from inside a custom OnGUI of a ScriptableWizard?