Filter/Limit Prompt Table Results with PeopleCode

Is there any way to accomplish this with PeopleCode? In most cases with a record/page etc I would either change it to a dropdown list and populate the list or change the prompt table to a view of my own.

BUT in this case I am working with a vanilla page housed in a custom component. Up to now we had this field as display only and were pushing a value into it (It is for a general deduction to be administered by a non-core group who are only allowed to see/enter the one type of deduction). But as all good things must these happy days have come to an end and now they need the option to choose between two dedcds. And the prompt table of course includes all the dedcds.