Years ago I think there was a tank for one of the LT's, but it wasn't much bigger.
Your only option is to custom build a tank, add an additional one elsewhere, or modify the existing one with a heat gun and pressurizing the tank.
Most limiting factor is the plastic over the tank...there's only so much room underneath it for a fuel tank.
If you don't care for the plastic, rip it off and bolt a bigger fuel tank on.