Vice grips did the trick
Thankfully there was enough of the broken bolt sticking out of the head to get a grip on... Unfortunately, I think during the process I screwed up the IMRC thingie (is the part where it looks like a throttle spring called the butterfly??) I also lost the retaining clip on the throttle cable... So all in all, engine runs great, except for the damned throttle (and I'll wait and see how the secondaries are behaving in the next day or so)
