Several weeks ago, a visitor to the local bike co-op described to me a sort of suicide hub he was riding on. The hub consisted of a standard screw-on freewheel hub with a track cog screwed onto it, and a bottom bracket lockring screwed on the outside of the cog to hold it in place.
I decided to give it a try. After two weeks, I am happy to report that this variety of suicide hub has worked well for me. The cog is still securely in place, and I have not experienced any "slipping cog".
So what does the FG community think? If this setup proves to be effective on a widespread scale, any screw-on freewheel hub could become a fixed-gear hub, no need for a track hub or rear wheel.