Trying to a payment module to dual process for preorders

Hi all,

I run a ZenCart shop and am adding a new product to my store, which will have extended lead times of 4-8 weeks.

Our desire is to allow pre-orders for these items, but, since the lead time is extended and price is high, we feel only justified in locking in the pre-order @ $50, and charging the rest of the cost upon shipment.

I need a module, even a paid one, that would allow our cart to charge $50 up front via paypal, and a remaining $500 or so upon shipment of the order.

Please, any help is most appreciated. I've tried to look thru payment modules and have not been successful in finding what I need. Any input or suggestions is most appreciated.

This, maybe:

http://www.zen-cart.com/index.php?main_page=product_contrib_info&products_id=588

I haven't used it.