I used to work in the online payment industry a few years ago. As far as I remember [things have probably changed though] is that first you authorize the payment, which means blocking the funds without actually withdrawing it. Looks like that is what you need. However, you are only allowed to block funds for about 7 days [or at least with most payment providers] and then the money has to be released or another auth. As I highlighted things have probably changed since I used to work in this field so I guess your best bet is to take your questions to a number of payment providers. This is not a question from coding side but rather form the legal side of things if I have understood correctly. Also do your homework! Throw a research on how things are done with kickstarter and the other crowd-funding platforms. go to linkedin. there are a number of groups which discuss or spam about online payment processing. They will be happy to help you. But do contact some payment providers directly and tell them what you are after.
I know I did not help you but I hope to at least have given you an idea on how to take this further.
Good luck and do share with us if you find anything further