The Screenwriters Guild (now the WGA) addressed this some time ago. Melvin Nimmer, who literally wrote The Book on Copyright, was their in-house counsel, and developed the idea of residuals, based on the theory that the Producers held the writers' copyrights "in trust."

I look at copyright, and have argued (though not to the point of a final decision) that the transfer of copyright, whether a work-for-hire or otherwise, is dependant on the payment for it. So if any payment is not made as agreed, the transfer of copyright is void.

This is the same theory as mechanic liens - workers put their labor into construction, and until they are paid in full, they have a lien on the property they worked on. I even filed a lawsuit to foreclose on Disneyland California Adventure, because some of the workers constructing it were not paid in full. Why can't the same theory be applied to the creative work that goes into the IP?