That's how I do too. If you haven't yet rabid, every so often check the odds of your other invaders. Swords and maces can take out CG archers easier then cats... or with better odds. Sometimes I suicide a cat into the city stack first, then switch to my invaders to take out the archers with CG promotions, then resume with cats.
Usually, you end up keeping more cats this way as CG archers are pretty tough initially. And the cats that remain get good xp for the next city you take.