Make a jumper plug. Get a DB25P (male) plug and jumper pins 4 and 5 together, then jumper pins 6, 8, and 20 together. Plug the jumper into the control and let 'er rip!
When the Fanuc control opens the serial port, it looks for a "high" signal on pins 6 (DR) and pin 8 (CD). If your 6-8-20 jumper is in place, then pin 20 will hold the other two pins high.
Fanucs also need to see a high on pin 5 (CTS). If CTS is not high, then the control will hang up when it tries to send anything. Jumpering pins 4 & 5 together will solve this problem.