It's even nastier if you're dealing with builds where they put Ammo in the Legs to keep it "safe".
So, Cripple with Leg Attacks. Then when it falls, or is slowed down enough, Swarm to start stripping the Mech apart.
It gets more interesting if you're using the Enhanced Flamer rule from The Battlemech Manual, and the Flamers do both Damage AND Heat.