Design a game — for best results, one that reliably produces fun play. Let's say the game is a 98-page PDF download or so.
Distill from that game a one-shot scenario and an abbreviated rule set that you can use to play through that scenario. Let's say the distillation is a 16-page PDF download.
Release the distillation for free, sell the full game for something reasonable ($10 download, cost-plus-ten Lulu print).
Sure, you could do this for lots of games. But for many of those games, the distilled one-shot would pretty much give away all the "secrets" of the full game. In other words, you'd be able to extrapolate the full game from the one-shot. Don't mistake me, I'm not thinking in terms of "people could cheat and not have to pay money for the game!" I'm thinking in terms of complexity and creative output. The trick of this is to make the full game sufficiently complex that it can not be contained in the distillation, but the powerful play experience, or at least one dose of it, must be portable enough to "fit" into the distillation.