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I had another idea for something that would actually lend itself... Precreate a bunch of cards, one to be locations/rooms/caves, etc. One set would be monsters and such, another set could be treasure, etc. The game progresses through the drawing of cards to creat random encounters, effects, challenges, etc.

It's certainly doable, but it will be a very different style of game to what you'd play with a DM.  I like Bohrdumb's idea, and it would potentially give you the best playing experience, but it would require a fair amount of setup.

Just putting together a party and playing through a module by yourself is another option if you want to keep prep to a minimum.  4e lends itself reasonably well to a style of play that is essentially a series of encounters strung together by a fairly linear plot.  If you're going to do this I'd suggest running with a smaller party than the adventure is designed for, as a big part of the enjoyment will be defeating difficult encounters and you're a lot more effective when there is a single person coordinating all of the PCs.