Yeah- that's definitely the proper way to do it. I once brewed 10 gallons of porter with a guy who did that to his half, and I dry-hopped my half (I'll admit now that his was the better one ). He was really into brewing lambics- even blended his guezes with some portion of 3-year old stuff- and had a good handle on how to do it. Essentially he just separated a gallon of the beer, innoculated it until he thought it was strong enough, pasteurized it and blended it back into the rest prior to bottling.
Sounds a lot like that guy I mentioned; he was really into lambic, geuze and saison techniques.
Right now I'm just waiting on my chocolate stout to finish fermenting (taking forever in this cold weather, my house is about the right temp to lager in on the ground floor!) and I just started a yeast culture from an interesting bottle of Scottish ale I found.
Next up: Making a metheglin from an old sherry concentrate kit I got on my last day of work. Should be interesting.