With regard to shipping bikes from London, Mailboxes Etc the US courier network have a number of outlets in the UK. Many of them in town centre locations.
If the guy packs the bike up, they will send it.
Here's their web address
http://www.mbe.co.uk/
If you find a store near him, try ringing them or your local US Branch.
The store near my office contacted one of their Italian offices on a similar mission a while ago and quoted me a price I could pay in the UK.
The alternative is to ask your usual courier company if they will do an overseas pick up.
You may even get away with US rates instead of UK ones, which are ludicrous. Almost $200 for a frame!
The South African who bought my Bartali last year arranged for it to be picked up and paid for it all in Joburg.
All I had to do is pack the bike.
Hope useful.
Alfredo Marcantonio
Twickenham England.