Hi Fred,
There is no Payment method delivered for Internal Transfer, apart from the one is displayed on the your screen shot which is for EU, and is obsolete. It also gives a message saying you can use SEPA credit transfer instead.
But you can create custom specific Payment Medium Formats in the Business Configuration, under "Outgoing Bank Transfer" and have an option to assign your own supplement code to Payment Methods.
To create Payment Medium format:
1. Go "Edit payment medium formats" and create a Z Payment Medium Format. Fill in all the basic informations
2. On the Supplement Codes, create a new supplement Code if its required.
3. Go to "Edit assignment of payment method details to your payment medium formats"
4. Here you can say the Payment Methods for which your payment format should be picked. Also assign your Supplement code as per the requirement.
5. After this follow other steps to create a custom specific structure before using the payment medium formats.
Hope this helps.
Thanks,
Santosh Kumar J