Without doubt, it can become complicated.

Terms: I agree to delegate you 25,000,000,000 RC's daily from my reserves. Lease expires automatically when your 'base' fully charged RC level reaches 50,000,000,000 (about 25-ish SP, I think). Using the "beneficiary" feature, at END of lease, I will be the beneficiary of 20% of your rewards until ______ (x amount) of SP has been paid as compensation for the delegation.

All the technical aspects would run in the background, programmed by the market maker. On the front end, all you see is the amount offered, the amount the triggers the end of the lease, and the "cost" of the lease via the "beneficaries" repayment. The "sellers" set the cost... and there would always be the "risk" that you get nothing because the borrower gives up, anyway. But the RCs were just going to waste anyway, so where's the loss?

Why have a "cost?" Simple psychology. People "value" something that has a price higher than something that's free... and so it would be a stimulant to encourage activity.

Just thinking out loud here...

=^..^=