Google Chrome and Firefox are starting to support the Gamepad API, and I've got code that turns a stock Arduino into a customizable gamepad ([UnoJoy!](http://UnoJoy.com)), so you can use it to get data from an Arduino into JavaScript. However, I'm trying to find a way to get data back into the Arduino.

Ideally, I'd like some kind of built-in USB hardware channel (like controlling the Scroll Lock keyboard LED) that can be hijacked to pass data, but [if push came to shove](http://en.wiktionary.org/wiki/when_push_comes_to_shove), being able to send data from the browser to an external client program would work (although I expect browser sandboxing to make that a difficult proposition...). Ideally, though, something that worked with nothing more than stock, stable-branch Chrome would be super awesome, so that people could just go to a website, see what they need to do with their Arduino to modify it, then be good to go.

Is there a sort of hack that might be able to leak information from JavaScript this way? 

I'm starting to think the camera API might give me some handles, but I'm looking for some other suggestions!