By sweeper, do you mean a sustained sweep or a hit-and-run Choice Item user?
sustained sweep.
Well, then you've got a hard road ahead. Unless you're being passed Speed and maybe some SpAttack, you'll have a hard time. Even then, your Special options are limited to Flamethrower, Fire Blast, Overheat, Shadow Ball, Trump Card, Hyper Beam, and Hidden Power. Oh, and Fire Spin, Ember, and Smog.
If I were you, I'd make a mixed Flareon. Something like:
Flareon @ White Herb
Overheat
Last Resort
Ability: Flash Fire
Nature: Lonely
EVs: 252 HP, some Defense to make up for the bad nature, and the rest wherever you feel is best.
I'd always hesitate to eschew a Pokémon's best stat, which is Attack in Flareon's case.