Swede - They are already performing this type of operation on a lot of the new AR models out there. Check out the H&K 416/417 as a leading example at the moment. Both are piston driven, and the piston is sealed to eliminate the gas tube "clogging" & the chamber "fouling" of Eugene Stoner's Design...
So, in answer top your question, yes. It's possible and it is in common practice on several new models. But, they are expensive as all hell here in the states and we can't even get access to the H&K stuff - but perhaps you could sell your right arm, buy one and give us all a range report?
An article I read recently stated that gas piston systems negatively affect accuracy. They induce vibration that doesn't exist with the gas tube direct impingment system. After shooting gas piston guns I tend to agree that this is a possibility, and would be a detriment to bench rest or competition shooters. On the battle field however, it would be a plus, since carbon fouling is not a concern on the AR-15 semi-auto rifle, but IS a concern in the M-4 or M-16 cycling hundreds of rounds a minute.
Ive seen one kit for shure to convert your own upper, advertised for $265
too bad the AR vents into the action, Ive had a MAS49/56 for a few years its a direct impingement weapon the gas on these are vented into a pocket on fwd top the bolt outside the action (no condensation problems like the AR's) ther kinda cool guns in a way.