There is no easy way around it. You either pay the premium or you don't. Sounds like you'd be better off just having supplies delivered if you will use it that little. My dump trailer has paid for itself over and over in the last year, but this is my full time job so I'm committed to it and pay the price to do it.
Taking parts off the trailer has nothing to do with the actual tagged weight of the unit. If you want to make money in this business you need to spend the money like the rest of us. There is no way to get around these costs but to cheat the system.