With about 30 seconds of thought.

You can still play the game without uploading so each game represents 2 copy's. Require an activation code to "load" the game which you can get automatically online or with a phone call. Require someone to unload the game which spits about a 6 digit code before you can upload it again. Make a fast online check to see if anyone registered the game via a partial code on the outside of the box for the used game market.

Don't let the disk play online content while "loaded" on a separate XBOX. Allow someone to declare an Xbox as broken, lost, or stolen.