Quantity based Billing plan

Hi All,

We have requirement that based on quantity need billing plan.

Example:-

SO 1234

Item                Quantity

10                     100

I need to billing based on Quantity like

Billing date          Quantity

30.01.2013            15

31.03.2013             35

15.04.2013             10

same like above user need do period billing for quantity.

FYI....In my project SD flow we are using order creation, billing and invoice. no delivery etc...

I checked below links but no answer.

http://scn.sap.com/thread/1459556

http://scn.sap.com/thread/1068805

Thanks,

Preddy