Could you ?
Yes.
Is it ideal?
No. But your not in an ideal situation. If it works(no guarantees as we don't know 100% why your FG is so high), you'll have quite a bit of sediment in your keg.
It would also add oxygen exposure, but if there is indeed fermentable sugar left, that should be mitigated.
You could also try adding some amylase enzyme. It+so5 helped me with an already kegged dipa stuck in the upper 30s. Mine got stuck from 002 flocing out before finished.
Ideally, you would want to either push the end result to a purged keg or let it crash in the keg for a bit then pour off a couple pints. If you ever moved or shook that keg, all the yeast would be in suspension again.
My lesson learned: take gravity readings before kegging. Krausen up, krausen down, wait a week(or two) doesn't always cut it with big brews. I wouldn't hesitate to pitch a starter in a stalled brew in the fermenter, bug in a keg presents far more issues. Your call. But if it is undrinkable to you now, you have to spur fermentation, or dump it.
The reason I don't want to transfer it again is to prevent oxidization. I just would like to let it sit in the hot garage over summer and do its thing.
It stalled because of my new brew bucket. I ramped temp up two degrees a day, once in morning and night, but once it hit 80 on my temp controller I noticed it would go to 81.5 then drop to 79 before it would kick on to heat back up. The placement of the probe or something messed things up. Bought two of them and after $450 I'm back to using my bottling buckets.
But anyhow I would like to fix this without transferring. Would a saison yeast work? In summer heat? I realize I don't want to potentially contaminate my system just to save one batch.