Well, and for those who want to add such stuff in a "super-easy" way, there's always IActiveScripting-interfaces,
which would then allow even simple Function-adding in a dynamic fashion.

Into an empty VB-Project with a Form1 - add a new Class with its default-name Class1 - and paste the following:
Code:
Option Explicit

Private SC As Object

Private Sub Class_Initialize()
  Set SC = CreateObject("MSScriptControl.ScriptControl")
      SC.Language = "VBScript"
      SC.AddCode "Public foo: foo = ""foo"""
      SC.AddCode "Public bar: bar = ""bar"""
End Sub

Public Function Dyn() As Object
  Set Dyn = SC.CodeObject
End Function

Public Sub AddProp(PropName$, Optional InitVal)
  SC.AddCode "Public " & PropName: If IsMissing(InitVal) Then Exit Sub
  If IsObject(InitVal) Then CallByName Dyn, PropName, VbSet, InitVal Else _
                            CallByName Dyn, PropName, VbLet, InitVal
End Sub
Public Sub AddFunc(FuncName$, Code$, Optional ParamList$)
  SC.AddCode "Function " & FuncName & "(" & ParamList & ")" _
              & vbCrLf & Code & vbCrLf & "End Function"
End Sub
Ok, and here's appropriate Test-Code for the Form:
Code:
Option Explicit
 
Private Sub Form_Load()
  Dim C1 As New Class1
  
  With C1.Dyn
    Debug.Print .foo, .bar 'those were ensured already at class_initialize
    
    C1.AddFunc "foobar", "foobar=foo+bar" 'add a new method
    Debug.Print foo, .bar, .foobar
    
    .foo = 1: .bar = 2 'Prop-Value-changes
    Debug.Print .foo, .bar, .foobar
    
    C1.AddProp "baz", "baz" 'add two more new properties
    C1.AddProp "Form", Me
    Debug.Print .baz, .Form.Caption
  End With
End Sub
Et voilà - there it is - a dynamically expandable Dispatch-Prop...

Olaf