I've had decent results starting lettuce in flats of plain old potting soil, under lights. It requires *religious* attention to the moisture level, don't ever let it dry out. This is tricky when you're using a fan to keep the temps down!
The first time I just let it grow in the flat, fascinated that it grew at all.
http://www.flickr.com/photos/10803470@N00/5468538794/
The second time I started fewer seeds, and when they got big enough, I scooped them out with a large spoon and transplanted into 4" squares.
I tried sprouting seeds in coffee filters and it worked the first time, then the next two times I was busier and let it get dry, so that was the end of that!
For my next attempt I'll use deeper square containers, I think it might be happier (more growth) if it has more room to grow roots.
I'm about ready to turn off the lights so I stuck the last seedlings outside, where they promptly melted in the heat. I had intended to give them a floating row cover, but, oh well. I think I'm done growing lettuce for a while, I'll try again in the winter.
-Wendy