Use an 'easy out'. Try to grind what's left flat, center punch, drill with the recommended bit, then use the easy out to remove what's left. I'd recommend the easy outs with the straight splines, much less likely to break in my experience. Also use heat, get it as close to red hot as you can without burning down the truck, first choice oxy/acet, second mapp gas, third propane. The hotter the flame, the less likely you'll catch the surrounding areas on fire. The bolt heats up before the surrounding areas do.
You may also be able to just drill it out with a bit close to the same size as the inner diameter as the bolt, as it's not a blind hole, the bit might catch in the bolt and drive it through.
Good luck,
Richard
edit, I see the other responses have you covered.