This should be possible since you can filter pages by trim size. Set a filter to accept pages with a trim size X in range of "size in points" and Y is in range of "size in points". I've found that it works better to give a size range instead of the exact size, since you sometimes run into rounding errors. So for a 6" width you'd want to use "305-307" instead of "306".
Depending on your version of Prinergy and how you apply the preps template, you might find that it works better to pass these values into a custom field, then set up a separate filter that reads the value of that field and sorts the files into the correct template accordingly.
When we did something like this for a digital workflow, I had it split pages produced from input files refined and then filtered those through a table of values in the set custom field action. Depending on size, a different value would go into a template custom field. Another part of the RBA read that custom field value (triggered by customer approval of all pages) and sent it to an output hotfolder.
Hope this helps
Shawn
