Originally Posted by pebadian

I have actually done exactly that and can confirm it works.

I've transferred the amount via bank transfer onto the account details that amex provides in the FAQ/Help section. You'll then basically be in "plus" and can pay something worth the "plus" and your normal credit limit (So you transfer 7k, you have a 5k limit, you can spend 12k)

It worked roughly a year ago, I wouldn't know why not anymore