In the past I've got round the need for a US zip code at gas stations by pre-paying at the kiosk. Sometimes they require a passport to validate the credit card and it can get a bit annoying if I forget it and have to scramble for other forms of ID.

I'm now trying to buy transport tickets online (for the flyaway bus from LAX to Union Station, from Metrolink) and am being asked for a zip code when paying with a UK credit card. I know I can queue up to buy a ticket at the kiosk when I arrive at Union Station, but it would be nice not to have to do that.

There are numerous discussions online about how to add zeros to the numbers in a UK post code, but I thought I'd contact my credit card companies for advice to see if they have an official policy.

Amex have said that I can change my account address to a USA address while travelling, then back to my UK address when I return home.

Before I do this, has anyone tried it and does it work?