The hex is 6MM. Buy a inexpensive 7MM hex. Using a hand file or small grinder put a slight taper on the leading edges of the hex. Drive the hex into the stripped hole with a hammer. If it wedges in tight heat the bar end with a heat gun to soften the thread locker that is applied at the factory and attempt to remove the bolt.
You might just get lucky. If not you are SOL.
Yes, the only other thing you can do is take it to someone that has brasing tips and torches, what you need to do is be a part of a team, one person heats the allen head cap screw red hot , you need to do this in 1 minute or less, the other person or you needs to have a wet rag in hand, wait about 1 minute and quench the bolt , this does two things , it helps, barley but it does help to harden the head, the very next thing you need to do is put your hex wrench in and try and turn this out. The purpose of the heat is to break the locktite down.
A third option that I have had considerable luck with is to go to your neares hardware and buy a hammer type impact driver, also get a coupling nut that closely matches the 6 to 7 mm, instead of buying a expensive allen head socket, use a metric socket or inch which ever fits the coupling nut and then fit the other end of the nut as previously described by filing etc.
To be clear, this impact driver is one that you twist with your left hand and hit with a hammer, I have removed Forklift grade ten bolts with this, should be less than $20, and comes with a 1/2 inch drive tip and various screwdriver tips.