It's possible, but may not be necessary if you can get this much simpler approach to work:
Base a list view layout on the portal's table and include field from your current layouts table in the header, footer or grand summary layout parts. As a List view, your layout will automatically adjust to print any number of records from your portal table all from a single layout. The trick is to use a script to pull up a found of just the related portal records for a given "parent" record from the table that your current layout is based on.
The Invoices Starter Solutions that come with FileMaker 11,12 or 13 all use this method for printing the line items portal of records on an Invoice so you can look at them for a more detailed picture of how you might set this up.
And yes, this isn't always an approach that you can use, so let me know if other considerations keep this option from working for you.
A little delayed, but now a report: Your suggestion put me on a new track, and after taking a new approach, I have solved my problem. Your mention of a list view (not a portal) was the key!
Without unnecessary details, I'll just say that I have scripted a method to find the job-specific line items and use a list view with great success. In retrospect, it's so obvious. Now I will polish the look of the payout for printing, but I have exactly the solution I was hoping for, and I dont have to keep recreating new pages to hold overflow. Perfect!
Thanks for your help.