We were both wrong by a little...
I tested my wife's Pace 350 this morning and it does not work from a stop, as I previously thought. I discovered you can get the throttle to work without pedaling, if you get the bike moving more than 3 MPH. I did this by pushing the bike and jumping on, and also by using my feet to propel me without using the pedals. Unlike the Pace 500, the throttle on the Pace 350 continues to work at any speed without pedaling unless you come to a complete stop, which then requires you to get the bike moving again.
Her 350 is a lot less powerful, so it does not have the same "surging feeling" that you get from the 500 when taking off with PAS 1. I like how my bike feels when it surges and she prefers the much softer feel of the 350, so we both got what we wanted.