I've done this for work with a newly setup card. The initial limit was low, but we needed to use it for a large amount of charges related to setting up a new office. We prepaid a large amount and AMEX had no issue with this, and then after a certain amount of time (90 days I believe) automatically refunded the slight overpayment that was left after that point. By that time the card had been used enough for the initial low limit to be removed.