Several hardware stores, even Sears, sells a wrench that looks like a miniature oil filter wrench. The head is an adjustable head that loops around the bolt. The more pressure you apply in turning the wrench, the more it grips.
Only problem is that you need a bit of elbow room. Another solution if space is an issue is a one-size-fits-all socket that you can use with your socket wrench. It looks like a regular socket on the outside, but inside has a bunch of spring loaded rods.
Dunno if it works but it's still a neat little tool....
Best of luck.