If the smart tool is selected, you should be able to drag/draw events into the pane.
If "Snap To" is enabled, then the events will only appear on snap divisions.
You can draw events with values from 0 to 127 and any value over 64 will be "Sustain down" and any value under 64 will be "Sustain up".
At least, that is how it appears to work for me.