I am a left AKA and have just bought an SE5.
For the parking brake I sometimes use my left hand (holding the left handlebar with the right hand), and some other times push the parking brake pedal down with the tip of my elbow-wrist crutch.
By the way..., anybody out there has ever come up with a solution to carry them crutches alongside the Spyder?
Cheers...
(Limitations just exist on your mind)