Prorata Billing problem

Hi,

A customer purchased a product created on first payment and recurred payment annually. Can he purchase the same product with prorata charging on the same end date of his first purchase? The order and invoice are automatically created by the customer ordering.

For example, assuming the payment for the 1st, 2nd and 3th purchase is 12/12/2012, 12/01/2013 and 12/04/2013 respectively.
1st Purchase for product A: 12/12/2012 - 11/12/2013 - $1200
2nd Purchase for product A: 12/01/2013 - 11/12/2013 - $1100 (calculated automatically)
3th Purchase for product A: 12/04/2013 - 11/12/2013 - $800 (calculated automatically)

Please advise the approach.
Thanks