This is one of the cooler pieces of code that I've come across in a while.
This technique is coded using VS Tools, but it was ported from VBA code so it'll run just fine in VBA. You'll have to edit the data access code in that case to use ADODB.
The object here is to place a dropdown list on a NATIVE Dynamics form (not one that you added using .NET) and then to populate the dropdown with data.
This piece of code uses 'Pass through SanScript' to do the deed. It's not too complicated and it works just fine, well worth studying.
If I've not explained it clearly please let me know, I'll help.