If you actually had an allen head CV bolt (some are allen and some are what they call 12 point or star drive) then you can buy a 12 point tool and drive that into the allen and you should get it out that way.  If this doesn't work, then get some "vice-grips" TM and try these.  If this doesn't work, a small amount of plastique explosives will do wonders on a stuck bolt (however the rest of your van may also come apart at the same time so use this as a last resort:).  

Hope this helps,
Ken Wilford
John 3:16
www.vanagain.com
Phone: (856)-765-1583
Fax: (856)-327-2242