Your typical 110v outlet is between 108 and 121 volts AC.
It will be on a 15 or 20 amp breaker.
You should not pull more than 80% of the rating of the breaker, so thats 12Amps.
So in theory, if nothing else is using the circuit (aka no coke machines, lights, etc) you can plug into most outlets and have 1300-1450 watts available at any outlet.
The onboard charger of the FX models is only 650watts... so you could double it to 1300 by adding a separate external 650 watt charger and plug it into the same outlet.
This cuts your charging time roughly in half and is fairly simple to do.
If you want to go faster than this, that is where it becomes tricky. See its not each outlet thats limited to 1300w... its the entire circuit. So unless you are POSITIVE that the second outlet nearby is on a separate breaker, you cannot plug anything else into this. This is where your hangup is. Its rare to have multiple outlets outside of one building on separate circuits.
So you can cut a 9hour charge down to 4.5 hours... but you're still waiting 4.5 hours. You are limited by the outlet.
If you use a generator, you will be running it at or near max power for however long... probably using more gas than just having a gas bike. The generator will have its wattage limit written on it (Not its peak, you need its continuous numbers)
You could use a car charging point with a more powerful charger, but you wont find that out in remote areas.