Special payment option

Hi, I use a cre loaded b2b 6.4 shop. I need you to create a special payment option that should work in this way: If a customers order total is below x $ he should only be able to pay with payment option A, if the customers order total is over x $ he should be able to pay with all the installed payment modules. I should from the admin-interface be able to set x (the split amount) and A the payment module that the customer should use if the order total is below X Please ask any question before bidding. Regards Søren