They look better than the threaded "easy outs" that go in after you drill a hole into the old bolt, but still - good luck.

Something to consider is to REALLY heat them up. Oxy-acetalene torch perhaps. If you get the bolt, and the surrounding area cherry red, then you do something interesting: Hot parts expand. The bolt will try to expand out into the area around it (the nut, or the part it's screwed into), and of course the threaded area will try to expand towards the bolts. When they run into each other (very quickly), they will have no choice but to stop expanding "that direction" and instead expand be forced to expand "up and down" - basically a different direction. This is good because they change their shapes a little bit, and once they cool off, they have now changed shape permanently. The threaded part will cool and pull slightly away from the bolt, and the bolt will cool and likewise pull away from whatever it's screwed into. You will hav now created a tiny gap, or at least taken some of the pressure off. Also, if you can, put a little candle or ski / snowboard wax on the pieces when they are starting to cool. The melted wax will wick in there and help keep the parts from sticking to each other.

We do this all the time here at work (Diesel engine remanufacturing plant). Workds great, just make sure to stop at "cherry red" or you may start changing the shapes of things more than you bargained for.