I would try a small intense heat source on the bolt first, something like a `jet` cigarette lighter or mini gas torch flame
Not keen on that idea - the glued joints are not far away.
After soaking for a day with plusgas I tried to remove the grub screw with a torx bit hammered into place. it was very firmly in and took a fair bit of torque before it gave up and rounded the hole. also, now the 'hex' hole is a bit larger i tried my 7mm extractor but it's still too big.