How to set up e-commerce shopping cart "pay shipping only" and full price after 30 days?

Hi all,

I was given a wonderful promotion idea by another member here, it is as follows:

Pay for shipping only (call it $6 for example's sake) and 30 days later, if you don't return it, your credit card is charged the full product price. (call is $50)

My set-up:
I have a shopping cart solution from shopify . com and paypal payments pro.

Shopify says they cannot do a split payment such as this - no way, no how. They don't store customer data for recurring payments, or at all for that matter.

Paypal says that for an additional $30 per month (on top of the fee for payments pro) they can set it up as a "re-occurring payment" where the payment plan will be:
$6 first month
$50 second month
And it expires after that.

Shopify cannot integrate this into my shopping cart, so it would be a plain paypal button.

Basically, I have no easy way to do this and maintain the clean interface that my shopping cart has.

Any ideas?

I am open to changing shopping carts as I am not happy with shopify for many reasons, anyway, and am willing to completely re-do the website if need be for the sake of a better shopping cart. (both to offer this discount, and to have a better cart overall).

Thanks!