Well, to be losing that much oil that quickly, there is either going to be oil showing on the outside of the engine, or oil going out the tail pipe. To determine if it is an external leak, clean the engine up and put a piece of cardboard under the engine where you park overnight. Won't take long for it to show up if that's where the leak is.
If the cardboard stays clean, you may have a leaking headgasket. Could be determined by pulling the spark plugs and checking for oil contamination. The 2.0L is not known to be an oil burner, and to go through a couple of quarts in 500 miles is definitely excessive. My bet is that when the plugs are pulled, one or more is going to have dark carbon build up.
If a dealer did the work, they should step up to the plate on this one. You didn't indicate why the head gasket was changed. Any possibility that the head was damaged?