Jimmyjet, I installed a 12v accessory adapter directly to my battery. I used this setup when I was running a GPS (Garmin 550c) on my trip to Nashville last July. I installed a ram mount on my left side handlebar.
I placed the 12v accessory socket behind the panel where the Triumph "BMW" powerlet socket would normally be installed. I then ran the 12v accessory cable for the Garmin from this socket up underneath the gas tank and tied it to the handlebar on the left side by the ram mount. It worked okay, but the ball set up for the ram mount was kind of "shallow" and didn't fit into the back of the Garmin socket receptacle as good as I would have liked. Hopefully your mount will be better suited for your unit.
In addition, as a side note, the new 2008 Tourer model has an optional GPS cable that can be mounted directly to the battery, not sure what type of plug at the end of it or what GPS unit it is designed for.
Hope this helps,
Dennis