I'd heard somewhere that Planxty were in a similar situation regarding (at least) their first couple of albums. Vaguely recall seeing a documentary where Andy Irvine was getting pretty angry about it.
I would have thought the simplest solution would be to simply say you can't sell the rights to something you've composed- only rent them out for a set period. An alternative would be to let artists veto the sale of rights to their material to other companies- I'm sure that could be arranged without huge difficulties. Big change though and it would piss the companies off no end.