It'd be most sensible to show up at multiple, carefully selected points in time.
For example all Xbox Live Arcade games are required to have a trial (demo) which can be seamlessly upgraded to the full version at anytime. Every trial is required to award the player an Xbox Live achievement and Xbox Live Avatar Item at some point. When receiving either a pop-up occurs saying "You've earned <X>, unlock the full game now to keep it". Or something to that effect. Then of course there is a final upsell at the end of the trial.
For example all Xbox Live Arcade games are required to have a trial (demo) which can be seamlessly upgraded to the full version at anytime. Every trial is required to award the player an Xbox Live achievement and Xbox Live Avatar Item at some point. When receiving either a pop-up occurs saying "You've earned <X>, unlock the full game now to keep it". Or something to that effect. Then of course there is a final upsell at the end of the trial.