Basically you need to use your Konsole and do the following:
sdptool browse <Bluetooth Device address>
That returns all services on your BT device.
Then look for your GPS item and what channel its on. Then do this:
rfcomm bind /dev/rfcomm0 <bdaddr> <rfchan>
That basically binds the BT device to /dev/rfcomm0. So then just go into your GPS program and tell it to use /dev/rfcomm0.
Works great. I did it to use my cell phone via bluetooth for "dialup" but it is actually pretty fast. I'm using a LG VX8100. Its great.
BTW, I just got this info here and reported my usage of it a few weeks ago.