rounded bolt off, HELP

[toyotaxr8]

i my job this is a daily occurrence the best way to remove it when the head is rounded and vice grips wont work is to get a nut and weld it to the bold head thorough the threaded hole set the welder amperage high to really penetrate the bolt fill the nut right up to the top then as the nut turns from red hot to black undo it as the heat from welding loosens the bolt with out putting much heat into the surrounding area. this trick has yet to fail me i have used it from 6mm bolts to 3 inch plus at work its also good if the bolt has broken and there is just not enough sticking out to get with vice grips.