Hi Andy,
I'm assuming that you'd like your second key to be able to unlock the car and start the engine. That being the case, I can think of a few options...
1) I'd be more than happy to sit on a flight to the USA. With my laptop and other tools, the world is your oyster. I could add cruise control or a variety of other things you might be missing.
2) If you're able to send your existing key, the instrument cluster, the central convenience unit and the engine management unit to the UK, then I can add a second key and post it all back to you. Your car would be stranded during this time.
3) I can create an engine management unit with the immobiliser disabled, which I could then post to you. Once you've fitted it to the car, all that's needed is to have a second key cut. As long as the blade rotates in the ignition barrel, it'll start the car. No computerised programming would be necessary.
The downside of the third option is that the second key would not work remotely; you'd have to insert the blade in the driver's door to gain access. It would very much be an emergency thing, used to get you out of trouble if you lost your primary key.
Let me know your thoughts. There's no one simple solution, but I'm happy to help.
Cheers,
Tom