This is an interesting idea, but I think for the risk that the lenders are going to be taking, they would have to charge sky high interest rates. (And maybe this is feasible). There's a reason brokers don't offer margin trading on penny stocks and junk bonds.
Lending money with junk bonds as collateral (for going long on the bonds) is impossible. But lending junk bonds with money as collateral (for shorting the bonds) is safe and useful.