Just passing through. John Hartford was a great one for keeping a rhythmic thing happening with his feet on a board while playing fiddle, banjo, guitar, or whatever else struck his fancy. I had the privilege of seeing him in performance twice, and it was a great experience. Wouldn't want to try it myself, though -- it looked tricky, and I'm sure it took a lot of practice.

However, I have also heard of an electronic device for sale that sounds a lot like what you're looking for. I don't remember what it's called ("Bass Board," maybe?), but it's basically a wooden board with a piezo transducer embedded in it, and a preamp, and you tap your foot on it as you play. It reportedly sounds almost like you have a bass playing with you; the sound is low-pitched enough that, in conjunction with your guitar (or other hand-played instrument), it fools the ear into thinking it's playing the proper bass note along with the rhythmic pulse. If I remember the name, I'll post a followup message. I know it's advertised in some of the acoustic music magazines, and I read a review of it in one that said it does pretty much what the manufacturer claims (I don't put a lot of trust in magazine reviews of music gear, but I thought it was worth passing this along anyway). Good luck finding what you're looking for, whether this is it or not. -- WS