If developers of Run.GPS software will implement complatibility with Polar SonicLink devices for WinMobile platform,
I recommend to look at open source project http://rs200-decoder.sourceforge.net/
this software has C code which is very easy for porting. Actually, this project for RS200 monitor but all others have the same algorithm of sound processing.
I think exporting HRM files is only possible with the high-end Polar models. It's probably not possible to use the sonic uplink from within the GPS-Sport.net portal.
You could get yourself the Oregon Scientific Heart Rate Logger (33 USD). We haven't tested it with the F6 yet but they say on the company website that the device is compatible with most analog and digital heart rate monitors.
I have the Polar F6 heart rate watch that uses the sonic uplink system to send its files to the Polarfitness web site, would it be possible to use the same system to upload the HR information to the Run.GPS site, I have only just bought this watch but it will not allow me to get hold of the HRM files.