Is there any way that the Rockets can trade away enough salary to just sign him outright?
This would be where the Celtics' $10 million exception could come in handy.
I think it even goes beyond this. The C's could facilitate a three-way trade to make this happen, if they can find a third team to take Lin (who I don't see the C's taking on). Lets say, for example that Brooklyn likes Lin. You can work out a three way deal.
Boston gets Asik, Marcus Thornton (expiring)
Brooklyn gets Lin
Houston gets Bogans, Pressey, Johnson (all could be cut immediately and come off the books)
Boston gets Asik, and a solid SG in Thornton, who could also be valuable to include in a bigger deal as an expiring contract.