Metronome is actually a function that was added into BeatBuddy while it was under development. Whether a special version of BeatBuddy is necessary or not - time will tell. Nice suggestion anyways!
I just built a couple of stomp pedals for left and right. They activate an Alesis DM5 drum module, so they can be assigned any of about 500 drum sounds. Just tap your foot along with any song you can play.