Actually you're right, we have provided no way to use the sustain pedal. Maybe in a future update we can add a "hold" button on the interface, which can be toggled with the MIDI sustain pedal or with the mouse.
There is also a question with the arpeggiator which is related: the "hold" mode of the Arpeggiator is currently saved in the presets, while maybe it would have been more logical if the arpeggiator was only ON or OFF, and went into the hold mode when the sustain pedal (or the "hold" button") is down and the arpeggiator is ON.