I seriously doubt that that you could get that many connected. Each mouse would have to have its own connection, and loading multiple drivers and mice could cause serious conflict. It might be possible (I wouldn't do it) to connect multiple mice through an externally powered USB hub. If you don't actually want the pointers to move, do a print screen of the desktop, paste it into a graphics editing program, then copy and paste the pointer all over the image. Save it and use it as the background.
edit: print screen does not capture the pointer.