NAB: How do I filter dropdown values on Form widget?

[jcallahan]

I've created a Form widget to present a list of available values from a table that may be assigned once per "entity".

I'd like to remove values from the dropdown that have already been assigned (i.e. if the possible rows are are A,B,C,D,E only present unassigned rows B,D E in the dropdown if A and C have already been assigned for the given "entity")

Doesn;t seem I can use the Helper Program program for this purpose