There is something I'm missing here. The OP is going on a hilly ride and he's changing the big ring?

Seems like the small ring which requires pulling the crank would be more useful to swap out. As far as removing the bolts goes, a screw extractor could be helpful. Blowtorch to heat the area might too. Did you not lube the threads?

In the OP's case, I'd recommend against drilling. While it should be effective, he sounds like the kind of guy that might get a bit of material from the spider as well as the bolts.