Probably won't have enough space but I had luck with a welder in the aluminum head of my 4G63 when I broke off an exhaust manifold stud.
Weld up a bead onto the broken stud, do it a little bit at a time, like 2-3 seconds of welding in a slow circle, tap it with a hammer or something (again, very tight space) and let it cool. Do the same thing over and over until you have a bead large enough to weld a washer on. Weld the washer in the same fashion, and make sure to completely fill the hole of the washer with weld. Now, weld a nut onto that washer and you should be able to get it out.
Old mechanic taught me this trick and he told me to just jeep trying, doesn't matter if you have to do it 10 times, just keep trying and eventually it will come out.
I had to do it 6 times, and I got better at welding the washers on / found better combinations of washer / nuts to use each time.
3 stages of removal
Pretty new fasteners
