If you have the correct voltage/impedance converters between your RS232 pins and the device you're driving it may be possible to write your own communications protocol using a control pin on the serial port.

Windows will let you switch DTR and RTS if I remember correctly using an API call, it is up to you to time this properly. Messy, but possible.

Actually, looking at the documentation for Win32API:CommPort there's an example of this very concept.

update: apologies I missed the fact that the device is standard serial 1200 baud. Thus you only need the RD pin wired up.. but follow the link g0n provided in Re: (OT) How to read a 2-Wire RS-232-C line? to ensure that the PC end has DTR/DSR/CD pins wired together and the RTS/CTS pins wired together (so the PC thinks something is connected to the port). Also ensure your device handles RS232 voltages (+/-25V). If it doesn't you'll need to add some hardware to convert those to CMOS voltages (if your device is CMOS) otherwise you might fry your component.