Double Post.
There's really nothing you can do that I can think of if you want it thoroughly cleaned. I suppose you can open the 360's system tray and unplug it (to keep the tray open) and use a powerful vacuum with a narrow slotted attachment and hope for the best, but I don't see how you'll be able to clean it out any better without opening the case. The Wii however, I don't know what to tell you.
Honestly, I'd feel like the benefits of cleaning the system outweigh voiding the warranty -- they probably did cost you all that much since you get them off of Craigslist after all. Are you sure they're even under warranty? Do you have the original receipt for them?
Man, this thread brings me back to the late 80's. I remember how full of roaches my stored consoles got. Urgh...so freaking nasty.
Cracking it open and physically cleaning the unit is likely your only option.
I'm not sure what the warranty covers precisely, but there's a good chance that having bugs inside is already a warranty-breaker.
Be careful about where you keep the units in the meantime. Maybe seal them off until you can clean them properly, outside of your home. The last thing anyone wants is to "inherit" someone else's bug problem. Roaches likely won't stick around in a clean house (no abundant food supply), but something like bed bugs could haunt you for years.