I’d go hard on the faux sympathy, treat him as a small child who has hurt himself. He’ll hate it. He’s trying to get under your skin, and power-play, so playing a pity game towards him will counter that.
‘Oh Graham, you seem so sad about this job ending. How can we help? Never mind, lots of free time to do things you prefer soon. Gosh, you seem extra stressed, is there someone we can call for you? Here, got you a biscuit. You seem so upset and I wanted to do something nice. I’m a bit worried, will you be ok? I’m hearing from everyone that you’re a bit out of sorts, Graham, what can we do to make it better for you in the short time left?
Not all at once, obviously. With a furrowed brow, head tilt and very very gentle tone. Perhaps a little pat on the arm, if you can stretch to it. He’ll soon shut his pie-hole.
I’d be handing him a brochure for local therapy services too, but I’m old enough to find these gits entertaining rather than upsetting. 