One possibility is the use of something like Happ's USB Game Control Interface (
http://www.happcontrols.com/joysticks/950800xx.htm). Basically, it breaks out a slew of raw I/O pins from the USB port, and it is HID compliant. It also fits under past years' cost allowances. There are a variety of buttons, switches, joysticks, and levers sold by Happ that are designed to work with it, but I would imagine that just about anything could be hooked up as long as the levels match up.