theoretically a boost bottle should help some, depending on its design (different volume affects different rpm range). But even better than that is using an extended intake length for an awesome resonance effect that will give you more power at low revs.
Legal restrictions usually limit either horsepower or engine size. If you stuff the crank, put a boost port in the cylinder, and hole the intake skirt of the piston then you will get a sizable peak power increase. But the cops don't know how much hp your engine outputs and they won't put it on a dyno to find out.