There are several ways that you could do this. One would be to buy two icade cabinets and you'd have 2 control panels. They do detach, albeit via screws. I use an ultimarch icade on mine, and I know there are some that have spinner capability. This could get expensive, as you'd need a seperate keyboard controller for each controller. All you'd need to do is detach the controller and remove the usb cable from the pi.
Another way would be to cut a rectangle out of the control panel, and mould your controllers out of separate pieces of wood that you slot in over the top of the icade control panel. You'd disconnect it in the same way as above, but instead of spending more money on another icade, you'd be able to create your own bespoke panels. Removed in the same way, disconnect usb and slide the controller out.