The idea is to allocate a COM port using information derived from the cable's physical location on USB instead of the serial number. If the cables are always plugged into the same USB port, then they will appear to the system as the same COM port.
FTDIBUS.SYS can be configured to use location information and the configuration parameter LocIds has been introduced for this purpose. LocIds is an array of device locations in the USB tree. If LocIds is set up, then only devices that are plugged into these locations are supported by the driver. So, if LocIds has been set up and a device is plugged into one of the supported locations, it will be installed as a COM port. If LocIds has been set up and a device is plugged into some other location, then it will not be installed as a COM port.