Found an easy way to wire my phone to the breakout. Found this battery tender USB hub on amazon for 10 bucks. Cable runs easily under the tank cover and comes out the other side. Just thought I'd post it here because I originally was gonna run it under the tank. Less chance of overheating this way

Also added a BT splitter so I can leave the hub under the seat and still throw it on the tender when I want to.

 

When I was looking for a solution on how to connect my phone/GPS I thought about the same thing you did. But I didn't like the idea of having a loose cable hanging around the handlebar in case you don't connect the phone, and with an 'open' connector/plug being exposed to rain.

Instead I bought an external battery pack with 13000 mAh capacity that I store in my handlebar-mounted tool back. Together with the internal battery this will keep the phone (Galaxy Note) operating for appr. 5 hrs with GPS on etc. In case I need to recharge while riding I connect a 3 amp USB connector to the battery tender plug and store it in my swingarm bag.

 

My battery tender hookup comes out under the seat on the right side. I went to radio shack and bought a battery tender style plug and about 2' of cable and a cigarette lighter plug. I can plug in and route the cable along the frame and into my saddle bag and charge my phone in the bag. Mine is on a heritage but would work the same if you have a breakout with a swingarm bag.

 

There is a cigarette bt adapter I used to use from Amazon for 4 bucks. Had that for about 3 years before it started corroding (sp?). Went this route to lower element exposure. Might look for a rubber cap to help with usb to element exposure

 

Optimate do one as well. Just wired it up today from the data port with the Harley adapter. Dealer put a Optimate pigtail on for me, which I don't use as I charge through my heated gear pigtail if I need to, so I took it off and crimped it onto the data port adapter, so it's only live with the ignition, and the optimate iPhone charger lights up purple when it's on, which is kinda stupid and kewl at the same time. Gives the under seat area a nice glow at night.