I see no practical way of doing that, A small jump starter or even any back up power supply that will generate enough juice to get you going that last mile or two is going to weigh pretty heavy in your back pack plus your charger on top of that. Unless you have a true 10 Amp fast charger which means you also need a 1500 watt inverter in your “power bank”. Your going to sit for ½ hour to try to charge it up, its just not going to work. It’s like taking a car battery in case your Tesla dies on the road - it’s not enough to make any significant difference.
Better you consider some range management thoughts. Take your charger with you, plug in for a while close to where you go from home before journeying back home. I would also try to figure out why your not getting over 30+ miles of range anyway on a scooter that has a stated range of 40 miles as its base specs. My Mantis 10 Pro easily will get me 40 miles on mixed driving driving modes, (Its 2 years old now, and has 3000 km’s on it) however i mainly keep it on one wheel, gear 3 - Turbo mode 95% of the time. Its plenty of power and speed for almost all driving conditions, even hills.
I can get home and back on my scooters round trip is 25 to 27 miles, but i just plug in at work anyway. It’s a free charge at work, and plans change and i may not go home after work. charging up to 90 or 95% given any opportunity, why not.