I could have welded a handle to it, but Instead I grabbed one of those damaged bolt-remover sets normally used on six-sided bolts or nuts that have rounded off.
Incredibly it worked! One of the set was almost right size. With the bolt head difficult to access, it needed a light tap with a hammer to get a little bite, but even at a light angle, it gripped that allen bolt no problem and out it came. A totally round head and it still came out.

There - you learn something new every day. Its not a tool I'd have considered for a job like that but was glad I had it. If you ever get a chewed allen bolt stuck in and you can't get in there to drill, try one of those broken bolt remover sets instead of easy-outs (which can break). Plus you get more torque with six bits of sharp metal gripping the outside rather than the inside of the bolt.
This sort of thing if you're not familiar with them:

Video here: http://www.youtube.com/watch?v=5ZP05y32aJw" onclick="window.open(this.href);return false;
Bought a stud extractor today. It'll come in handy.....

Maybe I should WIKI it.