New Payment module client specific

Hello all,

Our shop is now online and we got some questions for customers which have a billing account apart from our webshop
(we also got a store which you can visit)
Now is the question if it is possible to set a customer group on a diffrent billing system
for example
Customer A orders a item and can only choose between bank transfer or payment bij IDEAL/Paypal
Customer B is regular customer who wants an invoice once a month because they already have that in our store (not webshop)

Customer A is in customergroup "klantA"
Customer B is in customergroup "klantB"

How can I help customer B to get a invoice once a month but that customer A can use that type of payment.

I Hope you get my question, my Dutch is better than my English.