If your orders ars so light as to not need to make use of the individual weight tariffs within a shipping module then you can simply use the module and the min max order value, set your product weights to zero and bingo!
Most of my orders used to be less than 100g so all my shipping was by large letter 1st class (48p) - orders that exceeded £34 were automatically upgraded to special delivery. Things started getting complicated when the products exceeded the 25mm thickness dimension.... but that's another story!

Jonathan