Like others have said, you can carbonate your beer in a keg then hook it up to gas at the serving PSI when ready to serve. I did that with my last keg due to lack of room. 3 weeks later, when I had room, I hooked it up to gas at 10 PSI (ideal for me and my setup) and it was carbonated.
When you carbonate using priming sugar or any other type of sugar, you will use less than what you would use if you were bottling. For 5 gallons of a blonde ale, I would normally use about 4.2 oz of dextrose if I were bottling. In the keg, I used 2.10 oz of dextrose which I found from Beer Smith. I still picked 2.4 volumes of CO2, but it gave me the amount to use if I were bottling or kegging and not force carbonating with gas.
If you use too much priming sugar, you will over carbonate your beer and have foam issues when serving.