You will need a proper cascading script, like NATS or MPA3...there are a few others too. Please do a search on the main forum for cascading billing or for NATS and you should be able to get all the info you need.

please note these scripts are expensive and may involve monthly fees and you will have to pay your affiliates yourself (not via the biller's payment systems) thus the reason so many affiliate programs are linked to one biller.

cheers,
Luke