How can I set a Supplier's payment method to be Manual and apply to voucher?

We have a handful of suppliers that we will be paying via BPay through an online bank portal.  In PeopleSoft, how do I set the Supplier's payment method to be Manual and have that default into the voucher?  I get an error message that manual payment is not a valid payment method.  We don't want to set these suppliers' payment method to system check and then erroneously get picked up by a system check pay cycle; we want that payment method to to be manual.  On the respective vouchers, we would still use the payment action of record a payment