How to create variable sized booklets on the fly in Postscript

I am trying to enhance a production stream which is written in Postscript.
The goal is to produce booklets with varying contents and varying numbers of pages.
I want to do this from a single Postscript file that makes use of postscript forms (stored as arrays) that allow me to invoke a form, add variable information and then do a showpage.
All works well in terms of producing the 11"x17" spreads that I require. The files print without problem and can be distilled nicely into a PDF if required.
However, I am stuck in terms of how to direct each booklet individually to be stapled, folded and trimmed.
Production would be in a Kodak Digimaster environment.

In particular I want to issue setpagedevice commands that will somehow have these effects:
indicate the beginning of a group of pages that is to be stapled together, folded and trimmed
indicate the end of the group
(I am not repeating exact contents from one group to the next, so this is not a situation where "number of copies" is relevant.)

I would like to know where I can turn to find help with this problem.