Need sage advice on how to removing an old leaking hot water shut-off valve and salvage the nut. Can't budge the nut and has bimetal corrosion. Would anything work better than std penetrating oil or WD40?

Normally I would cut the pipe and install new nut, etc. Long story, but the pipe is inaccessible from both sides of the wall. Old built-in vanity cabinets - big project to move. Can reach the nut & valve with wrenches but not with saw or pipe cuttter without tearing out the cabinet.

Thanks in advance!

Fred