It's an interesting idea:

Is it possible to pay off a partyhat solely through lending it?

Well, I've decided to take this to the extreme and try to pay off a blue partyhat by lending it. I'll use this page to track my progress.

6/13/11: Lent at 5,000k for 24 hours
6/14/11: Lent at 1,000k for 10 hours
6/15/11: Lent at 1,000k for 5 hours
6/15/11: Lent at 400k for 2 hours
6/15/11: Lent at 1,000k for 5 hours
6/16/11: Lent at 400k for 2 hours
6/17/11: Lent at 200k for 1 hour
6/18/11: Lent at 4,800k for 24 hours
6/19/11: Lent at 200k for 1 hour
6/20/11: Lent at 800k for 4 hours
6/21/11: Lent at 400k for 2 hours
6/21/11: Lent at 800k for 4 hours
6/22/11: Lent at 200k for 1 hour
6/23/11: Lent at 400k for 2 hours
6/23/11: Lent at 1,000k for 5 hours
6/24/11: Lent at 400k for 2 hours
6/24/11: Lent at 200k for 1 hours
6/25/11: Lent at 200k for 1 hours
6/25/11: Lent at 200k for 1 hour
6/25/11: Lent at 2,000k for 10 hours
6/26/11: Lent at 200k for 1 hour
6/26/11: Lent at 200k for 1 hours
6/27/11: Lent at 400k for 2 hours
6/27/11: Lent at 200k for 1 hours
6/27/11: Lent at 1,000k for 5 hour

Totals: 22,600k for 117 hours