If you set up the document to use a specific tray for the first page and a
different tray for the rest and then insert Next Page section breaks between
bills, you'll get the effect you want (since the tray settings will be used
for each section. What you'll need to do is figure out how to insert the
section breaks automatically. If you can identify specific text that always
occurs at the beginning of a bill, you can use Find and Replace to do your
dirty work:

1. Insert a Next Page section break, select it, and Copy.

2. In the "Find what" box of the Replace dialog, type the text that begins
each bill.

3. In the "Replace with" box, type ^c^&. ^c inserts the contents of the
Clipboard; ^& inserts the "Find What Text," that is, what you were searching
for. The result will be your section break inserted before the text.