On the other hand, from a purely musical point of view…
I just tried playing a bit of rubato piano (and using the sustain pedal), while also tapping out the beats with my left foot… maybe it’s just that I would make an awful drummer ( 
), but I found the physical co-ordination horrible… really distracted from what I was trying to play.
Maybe another possible solution would be to use a microphone, and record mouth noises for the beats (then auto detect hit points etc)… I haven’t tried that 
.
Or, of course, then go through the audio “mouth” track with the TimeWarp tool . (and so the circle is complete 
)