You might get away with soaking them with some sort of penetrating oil (Kroil, PB Blaster ect) but I would estimate your chances of that working as slim if they are really bonded in there.

You might as well break out the torch. It is probably the best and easiest way to get it done. Those bolts are very intimately associated with that rubber and are not going to give up very easily.

Good Luck,
Michael