Real bad idea. You never want to weld onto a steel bolt, especially one made of soft mild steel that is threaded into aluminum.I wouldn't even think of drilling it. Spot weld a nut on the end of the plug and loosen as normal. Don't have a welder? An independent shop shouldn't charge more than a few bucks and 2-3 minutes to spot the nut on there. EZ outs are usually more trouble than they are worth. If the plug was tight enough to strip the head you'll prolly just bust off the EZ out anyways...
Those look pretty cool, have you ever used them? Interesting design, Ive never seen anything like those. If you can back it up with experience I might get a set.EZ outs should work as long as you have any kind of basic skills.
There are also bolt/nut extractors like these that don't require any drilling.