Bicycle Mechanics - Stuck headset cap bolt

Maybe I used the wrong size hex key (mixed up metric with imperial sizes), now the hex socket bolt, the one that goes through a hole in the stem cap and fastens it to the headset, won't turn loose because it looks like the hex socket is stripped pretty bad, turning into more round than hex shape. I need to change my stem and now is stuck. Any one have suggestions what I should do, take it down to the LBS and have them try it, or is there a DIY solution (I've been thinking about the nuclear solution of epoxy a hex key to it, but hope there is an easier way)?

Go to a hardware store and get one of those extractor drill bits. They drill into the head of the bolt counter-clockwise and when it grips it will unscrew the bolt.

or...

...take a dremel tool and either grind or cut away the top cap then use a vicegrip to remove the bolt.

drill it out past the cap

or buy the extractorbits

Or take a slightly larger size hex key, jam it in there to unscrew and discard the bolt afterwards...

Distroing the bolt and cap are an easy fix since both can be replaced cheaply.

A cut off wheel or hacksaw could be used to cut a slot across the bolt head (and will also cut the cap) so the bolt can be removed with a screwdriver.