What I have in mind is for Badspot to host demo servers, basicly ones that uses default gamemodes, and that when a demo player clicks join game on the menu, instead of opening the usual Server List it will open up a list of gamemodes he can join, and by clicking one will bring him to the server
Everytime the demo player closes the game, a screen showing features and reasons to buy the full game, with a link of the website or maybe a video.