I guess this is kind of a weird suggestion and maybe not really worth doing, but I can't not talk about it now. Am I the only one who (in my unfortunately brief playtesting experience) tried out CM with Secret Sword? It's a pretty funky idea, I know, and the calcs I did with it prior to testing it were not exactly encouraging. But it does hit the normally specially defensive Jirachi and Heatran harder than Hidden Power Fighting does, which might be more helpful for CM in rain, I guess. You could use Giga Drain or Pain Split for the last move as Shrang said, or use a Hidden Power.
A lot of this is going off of memory from months back, and I don't remember any of the relevant calcs, so I'm just putting it out there.