I remember a while back reading about certain shotguns that were specifically designed for "police-use" because they had no trigger disconnect (not sure if I'm using the right phrase here).

Basically is there a way that I myself or a qualified gun smith could modify a remington 870 express to allow for rapid follow-up shots.

i.e. When firing, if the trigger is held down when charging a new shell the shotgun would then fire again and so on until empty.