Yep you can bulk prime a keg, but why would you want to? The whole idea of kegging is to make things simple and easy, clean and quick. IMHO, I wouldn't even consider it.
Firstly, you would need to work out priming sugar amounts and add the sterilised priming liquid to the keg, then transfer wait 2 weeks or however long it takes to carbonate. You will no doubt end up with yeast replication and the formation of a yeast deposit. If you've just lagererd your beer for 2 months and it is crystal clear, and there is minimal yeast left in suspension-why would you want to add sugar to wake the yeasties up so they can start floating round in your beer making it cloudy again and while you sit back and wait for the thing to clear again. Then pour a couple of glasses of yeasty beer when you tap the keg.
By force carbonation you can hook up the gas, chill your beer and have a proper carbonated tasting the next day if you want. Your beers on tap and ready to go, and secondly it's beautifully clear. If it's a lager thats been lagering for the last 2 months this is even more important than you can imagine. Your beer is clear and ready to drink. Put some gas into it and get drinking.
Forget about conserving your CO2, it lasts forever even with liberal use purging vessels, force carbing and using CO2 to push beer between kegs. Plus, Australia hasn't even signed the Kyoto Greenhouse emissions. Force carb and wave goodbye to bottles.