I'm not too familiar with what that board can handle, but I'm sure some kind of Li-ion or maybe even Li-Fe setup can work for it. I've only ever done Li-ion on my gen.1 and have used the two AA batteries for it. That might be more difficult to secure on the bottom of the truck, so you might be able to try 4 AAA Li-ion cells. You would have to modify the stock battery tray similar to this:
http://www.atomicmods.com/kb_results.asp?ID=44 but it would be a really clean/effective way to add lithium.