Is it against TOS to have more than one publisher id on a page? It's fine to share via rotation, but can you have two ad units belonging to two people on the same page?
You could always set up a channel for the second person and pay them what they've earned at the end of the month, though granted that can get more complicated with taxes and what not.
Actually, having two different publisher IDs on the same page is NOT against the tos. I emailed adsense support with the same question.