Hi Eric,
Yes it is true. The process is called DNC. There are several cnc editor programs out there that will perform this function. As a matter of fact, I believe that Onecnc is giving away a free copy of their NCLink software, which would permit you to do this. Check at onecnc.net for it.
It will be necessary to build a comm cable (if the machine does not have one) and to get ahold of the comm setup parameters so you can do this. But a resourceful guy like you will have no trouble doing that, I'm sure