A great idea, though toribash is very limited when it comes to modding. Yes you can just have one square object that can bounce up and down for a single trampoline but it would be incredibly difficult to actually control your tori.
I say this due to elasticity of a trampoline and how you jump on one. Now if it were 6 squares connected by joints to make one section, it may work. Even then it is hard to say if it will work properly.
Remember, we only have 16 objects that are non-static to use out of the 120. ( for some stupid reason.. ) .