I can think of 2 solutions - 1 Finale, the other printer.Finale: Create 1 document for the 2 extracted parts using Finale's page layout & other settings (transpositions, measure numbers, etc.) to get it right. It's a bit user-intensive, but it will work.
Printer: Some printer drivers have "1-up," "2-up," & "4-up" options for the tree-friendly crowd. They work as you describe (putting 1, 2, or 4 pages of a document on one page), but again you need to have all of the information in one document.
I do not know of any solution for printing separate documents (as in extracted parts) on one sheet of paper - short of reloading the paper for a second run.
Anyone with other solutions?