As far as I know you can't do that. But. you should contact Amazon's customer support just in case.
You guys obviously have an account with them, is it possible for you guys to get me the credits if I can get Customer Service at Amazon to add it to your account? Maybe if I sent a support ticket with my receipt?
EDIT:
I just talked with their customer service rep, and they said I cannot use this unless you guys have the item for sell on their site. Do you have ad credits listed as a purchasable item?
If not, can this happen? I feel limited already now that Pay-Pal is not an option. I'd like to see some flexibility if this is a possible option.