If I understand correctly, you want to show different subsets when user is viewing the report or when the user is printing the report.
The row set of an Active Form is driven by either a subset or a mdx.
You could try to use two subsets, one for viewing the report and one for printing.
When Canvas print a page into PDF, it uses the current URL. You could store the subset you want to use for printing in the URL. And use the subset in the URL to drive the row set when printing.
To see how to update the URL, you should check the following article: