I understand a lot of reasons not to do this. But I think I would, provided that 1) Lynch was okay being part of a mutli-part backfield and 2) could be counted on to go full beast mode knowing that he's gonna get cut. And actually, the fact that either way (whether he stays or goes in Seattle) this has basically turned into a contract year again for him, I think you can assume he'd go all out. Being on, potentially, the last two SB champs would be good for negotiation I would think.
I don't think that Gray having one good showing is a good enough reason to shun a potential acquisition of any Lynch-caliber RB. Brandon Bolden had a game or two a couple years back where he looked explosive. Not saying Gray is crap, just saying if you have this opportunity, he's not enough of a reason to say no.
But he's not on the block. Which is why you let word leak out of your team HQ that this is his last year with your team 2 days before the trade deadline.