I have a recollection of some Linux drivers for winmodems going to the effort of faking a Hayes command set within the driver, and then faking a ttyS device so it would look exactly like a normal modem.

That's making the big assumption that he uses Linux. Under windows you probably have to call some silly "get_win_handle_for_serial_devices_no_not those_,_the_other_ones()". That's just a guess, of course.