If the issue with JimmyG is his cap hit, why not just restructure his contract to convert his salary to bonus and add void years at the end?
Except, I looked at their cap and they have $19.7M (9th highest) with 76 players under contract and 9 draft picks (1-#3, 2-#43, 3-#102, 4-#117, three in 5th, a 6th & a 7th).
With many of their injured players coming back incl. Jimmy, the #3 pick for their QBOF, plenty of cap space left; the 49ers are in excellent position to be a contender THIS year.
They don't have to risk putting their QBOF out there on WK-1. Maybe they pull a Flores and play the rookie after WK-8 depending on his development and Jimmy's play, but Flores ended up bringing Fitz back a few times because Tua wasn't ready yet. Maybe they trade Jimmy by the Nov. trade deadline. Who knows.
The point is, Lynch isn't just going to gift JimmyG to Bill. He's probably on thin ice as it is. He really doesn't need to do anything at this point.