Regarding the Risks
Yes I think it could be possible for you to find someone willing to drive your car back. As MarkMayo suggested there are a few options out there including organised services, as well as other travellers' forums (LonelyPlanet, etc).
In the case of an organised service such as Transfercar I would assume they have all the legalese figured out for you. However, in the case of a more social globetrotter-to-globetrotter organisatio, the question is would you trust a complete stranger to return a vehicle you rented? I would consider the safety and economical risks this involves.
Speeding and Other Tickets
First and foremost as MarkMayo again duly pointed out is the fact that the car would be registered in your name, so you might end up getting road tickets without you being the driver.
More importantly though is the fact that being you the only registered driver only you would be legally allowed to drive the car. This is true both from an insurance point of view (very important), as well as a criminal point of view (very very important). Imagine how much you'd have to pay if the return driver crashed the car. Even worse, imagine the return driver being stopped by the Police for routine controls. I think the Police would immediately assume the car to be stolen, and they would be right to do so.
Of course I agree that your fellow globetrotters would have no interest in wrecking the car or driving through all the red lights in America. However the situations I mentioned are the classical unexpected glitches that never happen but when they do someone ends in big trouble.
So the bottom line is that the safety of such a procedure depends on the legal small print of the rental contract you sign.
Registering Drivers In Absentia
I know that Hertz/Europcar and others require you to register all authorised drivers for insurance purposes. I never tried registering a driver that was not physically there with me when signing the contract. It might be possible though. You could call and ask. This would solve the insurance and police control problem. It would not however guarantee that you don't end up paying for someone else's speeding ticket, as I believe the fine would be addressed to the person signing the contract.