I have a portal request for managers to order food for their teams.  Each vendor has a minimum number of meals which can be different.  I have a field called 'number_of_people which determines which qualifies the vendor query.  I created a script include which returns the generated reference qualifier. 

Here is how it's set up:

Reference Variable

Script Include:

This works like a charm.  I used Will's PowerPoint posted above as a reference.