lol.
ive had this happen a couple of times in the past. what you can do that usually works is get all the other bolts out, use a prybar or a wedge to get between the ride plate and the hull as tight as you can without breaking anything. then use an pneumatic impact to try to remove the bolt, while putting pressure on the prybar.
once you have it out, i used two part epoxy in a tube small enough to go up in the hole, squeezed it in there as best i could. then put a fair amount of grease on a clean bolt, threaded it up into the insert so it doesnt ruin the threads, and pulled it out before it completely dried.
let us know how it works out for you.