I'm assuming your only doing ales here - Your best bet is to crash for 3 - 5 days, keg in your spare keg, put it on gas if you have a spare co2 tank. If you don't have a spare co2 tank, you can disconnect the tank from your active kegs, connect it up to your spare keg (now full of beer), turn up the pressure to 25 or so and shake a bit. Leave it there during the day when your not drinking from the active kegs (or several days if you can manage). reduce the pressure and reconnect to your active kegs. There is a lot more on this in the stickies in the kegging section.
If you can swing it - keep an eye on craigslist for a spare co2 tank so you can just use the set it and forget it mode to carbonate.