PayPal seem to have added support for this using a combination of Parallel and Preapproved payments: https://developer.paypal.com/docs/classic/lifecycle/crowdfunding/
The application model used in this document implements a crowdfunding
platform that lets project owners register and manage individual
crowdfunding events. Event customers are those who contribute to the
fundraiser. In this application model, the platform owner stands as a
business entity that is separate from the project owners who conduct
the crowdfunding events.
A crowdfunding application must use preapproved payments with defined
terms for the event contributions. Preapprovals provide the ideal
funding flow for all-or-nothing crowdfunding models; no money
exchanges hands until the fundraising target is reached. By providing
defined terms, you minimize fraud risk by providing a controlled
environment where the payment receiver, the maximum fundraising
duration, and the maximum contribution amount and frequency are
determined before the event begins.
Depending on the specifics of your fundraising model, you must use
preapproved payments coupled with either parallel payments or chained
payments to distribute funds to the different recipients. These models
allow for each PayPal account involved in a crowdfunding transaction
to receive different shares of the transaction amount.
Both payment flows avoid the issue of aggregation, which occurs when
funds are allowed to accumulate in an intermediate account before
being passed to the end recipient. PayPal's chained and parallel
payment flows provide visibility to all parties in a transaction, and
the end recipient (the project owner) must be named in each of these
payment methods.
I know this is probably a bit late for you, but in case anyone else comes across it...