Extending the USB Socket

Has anyone got any tips or recommendations on installing a USB socket onto the handlebars and taking a feed from the USB socket under the seat.

What Bike? I ran an optimate charging plug from the battery and bought a usb adapter, problem is finding a waterproof one. I just use it for the phone so have a charger cable taped to it.

Ride magazine this month rate the Ultimateaddons charger.