More proof that Prosper carefully monitors everything that happens here -- from Prosper's latest email blitz on this promotion:
* We reserve the right to disqualify any participant who attempts to abuse this promotion, as determined by us at our sole discretion.

Prosper also changed the minimum to $1,000, and made it so that only the lender's first bid per listing will be counted toward the promotion.
Note how different Prosper's attitude is from Lending Club. When Lending Club had a promotion and people thought they saw a deal, Lending Club said "Sure, go ahead. We hope you keep the money in, but the deal was the deal."
Meanwhile Prosper is on the hunt to arbitrarily dismiss any lender's claims to a valid application of the promotion.
I don't think Prosper has much to worry about people using this deal. No one trusts them anymore to keep to their word.