You can start and stop the sequencer using a footswitch.
With a footswitch connected to your Pro 2, enter the global menu and scroll down to "Footswitch Function." Select the option "Seq Start/Stop." Also: make sure that pedal polarity is set correctly for your footswitch. If it doesn't behave as expected, scroll down to "Pedal Polarity" in the global menu and change the current setting.
You should also make sure that the correct sequencer settings are being used. Play Source needs to be "Sequencer," Play Mode needs to be "Normal," and Restart and Env Trig/Step should both be set to "On."