Under one of the side covers (I think it's the left side when sitting on the bike), there's a spare connecter on the standard that is controlled by the switch. I wired my belly tank to it.
You could use this connection to run a set of wires up to your GPS mount.
Or, you could always install an after market fuse box which normally gives you more than one connection.
+1
That connector is ON and OFF as you switch the key and is perfect for the GPS.
You find the connector in the instructions book for your bike, and the wire is easy to lay along side the fuel tank and further to the handle bar

As you get more "extras" on your bike, you "build" further from this