inverse kvm?

We are all familiar with KVM switches, using a single console to control multiple computers. What I have been asked to do is find a similar switchbox that will allow one PC to be controlled by two different sets of keyboard/monitor/mouse -- so thatwhen the room is locked, one particular machine can still be accessed from outside the room (manufacturing environment). It is assumed this will be cheaper than purchasing/building another PC to sit outside the room. However, I have never seen or heard of such a device that I can recall, so I don't know if it even exists, let alone how much it would cost. I have found a keyboard splitter, and a mouse splitter (2 keyboards/mice --> 1 PC), but they are $50 ea., which seems a bit steep to me. I'd also like to avoid any OS/VGA driver/multiple-monitor-support issues, and not have to install a second display adapter (thus keeping the issue simple and cut-and-dry) if possible. I thought before I start searching every KVM switch mfr. I can find, I would throw the question out to fellow techs and see if anyone has come across this type of thing before.