carbide bit in a die grinder and hold on tightly, was the only way I could drill the D60 stud. You can try drilling a hole, heat it with a torch, then burn another nut on. Hopefully the weld melts into the hole and to the nut. If that doesn't work, a no other way of welding a nut to it will. (unless you start playing with fire and cold water, which I know nothing about) The carbide will still cut through the weld if it doesn't work, meaning an EZ out can still be tried. Get the biggest EZ out that fits and use the carbide to drill the hole out for it.
also, are we sure the crank is worth saving?
edit: make sure everything is clean, grind the end of the bolt a little for fresh steal.