We've been using paper types as our method for selecting trays. Plain paper is specified for all drawers, except perf stock in one specific drawer. Then in design's page properties, under advanced paper handling, we have rules like:

Section: Paper Type, Selection Plain 1 (80-90 gsm), Condition: =&perf <>1

and a second rule

Section: Paper Type, Selection Recycled 2 (80-90 gsm), Condition: =&perf = 1

We set this rule on each page, changing the page number as needed. This does happen to be a document where we have 6 document pages defined and any one of the 6 might be on perfed stock.

We set the variable &perf when we read in the record so that it gets turned on for the correct page.