Drill a hole and use an extractor...should have them at local hardware store. They look like a soft ice cream cone swirrell...you know the tool? That might get you the 'bite' you need...you just need to be able to drill a hole in the center of the bolt. Start with a smaller pilot hole...then make it bigger for extractor...
But, as you can drive it, a shop should be able to figure something out and shouldn't take them more than an hour, I wouldn't think. I don't know, but that's an educated guess.
GL...and GL at the autocross!