I'm sure you could, but that is a lot of engine for a secondary system. I'm not sure it would work on less than 36volts it is a controller system some of them shut down if the voltage drops.
This is the motor I sold on ebay. I have two more like it. They are twenty four volt. They will also run on 12 volt but only half the power. It is the kind of system I can put on my bike tomorrow and just might do that. You have me thinking that way again.
electric bike motor kit (sorta) - eBay (item 230233755933 end time Mar-26-08 08:17:59 PDT)
If I get this and it works, I might go looking for a smaller batter say two 12 volt five amp hour batteries. That would cut my weight by about 30 percent. I have a luggage rack on the back of my bike that would support the batteries. Since I run a twenty inch wheel on the bike the center of gravity would be lower. It might workout pretty well.
I'll give it a try just to experiment and let you know how it goes.