I have, made of a section of 2x4 cut in half and some scrap plywood and 1x2 board. There is also a towel taped to the bottom, so it doesn't scratch the wood chair I sometimes use it with. I works really well, because it goes UNDER your legs too, and it gives lots of added support. Rather than squeezing with your legs, your weight holds it up, and it does it really well.
Speaking of Logitech's Lap Attachment, could anyone comment on it, or show a picture of it? I'm pretty dry on ideas about where to mount my DFP after my first setup broke.