We did this at our small dev/design studio for about 5 years. It worked amazingly well. The contractors always had work and the "contract agent" got 10% of the contract in perpetuity.

The downside was that we were a fairly small operation and so we only had one agent. When he left to pursue his own business venture we were unsuccessful at replacing him and ended up closing up shop.

A platform that facilitated this type of arrangement would be valuable indeed...