I just pulled out this info - it's not clear which form! The wording is "... so not to waste time at the airport foreign exchange desks, one can simply indicate on the form that they would like the refund to be credited to their AMEX card." I assume this means on the form the store gives you. The info I received also gives a link to amex.com/traveltips.
It seems as though it would be easier to have all the refunds come to one place.
