Given than the bolt needs replacing & an allen key is cheap, try glueing. Once set, use pliers or mole grips with a sharp snap to break the tension as previously suggested.
Depends how stripped it is. Superglue or epoxy.glueing with what ?
Not sure you saw my suggestion. I recently churned up a hex bolt - smaller than those - it was an M4.
How I got it out was to us an imperial 3/16" allen key which is about 4.76mm. I found this sat in the churned up 4mm hex well enough to undo the bolt.
Cheers,
Nigel