I used to put the UEC cleaner in via the throttle body on my NA 2.5 Forester, I would get it warmed up, loosen off the clamp for the air intake hose enough to get the spray nozzle extension in there and spray 1/2 a can in and let it sit for 15 - 20 mins, then fire it up and put the remainder in whilst keeping the revs up. Then take it for a good run pushing the revs up in each of the lower gears.

I don't know if the turbo Subaru's have to be done differently.