Click on the controller you want to use for sustain (hold), and then enter the following data:
Assign Message: Channel Message
Type: Control Change
MIDI Channel: 1
Control Number: 64
Min Value: 0
Max Value: 127
Output Port: Port 1
Button Mode: Latch
Assign Message: Channel Message
Type: Control Change
MIDI Channel: 1
Control Number: 64
Min Value: 0
Max Value: 127
Output Port: Port 1
Button Mode: Latch