There are probably better solutions than what I'm writing below. At least this method works without any special options installed.
The robot webserver is accessible on the PC when using roboguide. 127.0.0.1 (localhost) for most setups.
When you go to this address in your browser, look for the POSREG file.
This file shows the current values of all the position registers.
You could create a script to periodically request this page and read off the coordinates and save them to file.
I've successfully used this method for debugging before.