Try this...if you can.
Set the sync button to "Start", then assign the start stop to a footswitch. You need to hit the f/s to stop it and thenext press of the keys will start it.
ie:

There's nothing you can do that can't be done....

On the word "done" ... you begin counting a 3/4 measure. Hit the stop switch on beat 3 - the next key press will then become downbeat ONE in a 4/4 measure.