Busy weekend! First, I changed the handle bar grips. Now I've installed a USB charger. 😎 

⚡ Before I begin, I just want to say that this is a procedure for people with experience working on electrical circuits. Do not attempt this unless you fully understand what you're doing; it could cause damage to the bike, cause injury to you, damage your battery, damage your phone, and/or void your warranty. So don't do this. ⚡

That said, here's how I did it. 

I bought this USB charger from Amazon. It converts 12 V to 5 V. It comes in two pieces: the connector wire that needs to be connect to 12 V power and the module; the charger module itself.

The connector wire has loop connectors on one end, which I cut off for soldering, and a standard SAE type power connector on the other.

Now, here's the messy bit that might void your warranty. The silver box near the power button (accessible by removing all right-side farings) is a voltage rectifier. It converts ~60 V to 12 V and outputs only when the bike is on.

I cut and stripped the black (-) and yellow (+12 V) and soldered them: interweave the exposed ends and wrap the lead from the charger's connector wires around the appropriate power leads.

Negative connects to the black wire (-); positive connects to the yellow wire (+12 V).

After making a solid solder join, I painted the splices with liquid insulator (shown) and then wrapped everything tightly in electrical tape until nothing moves. 

I used sticky velcro strips to attach the charger end to the inside of the compartment lid. The other end plugs into the SAE plug on the connector wire that is spliced to the TC's voltage rectifier.

This blurry photo shows me charging my e-book reader by USB.

Don't get ticketed for distracted driving. Leave your devices inside the bike's glove box.