I always fill my kegs with CO2 before filling, then connect the CO2 line afterwards and vent the top several times, just to get any additional O2 out of there.
I've had big beers kegged up for a good 6 months. IPAs won't taste the same after a month, but you might not mind. Hop flavor/aroma ages out pretty quickly.
If you keep the O2 out, and keep it cold, you'll never have a beer actually go bad. If you don't like some of the tastes that are developing, have some friends come over, and tell them it all needs to be gone in a night!