Re: I'm still trying to wrap my head around these bikes
A regular 2 stroke 50cc could work; depending on the steepness of the hill, my bike doesn't go up without me assisting it.
The only problem is, if you're just going to start it just before a hill, then shut it off or whatnot, it's quite pointless, unless you plan on having the clutch down to free-ride, whilst the motor is running, and only letting it pull you up on the hills, you're just wasting fuel on the ride.
Of course, if it's a very hilly area, it may work...
Depending on the topography of the bike path you do, it may be better to just ride normally and lower the gears on the hills to make the climb easier, though slower, and just having a motorised bike for fun during your spare time.