Store credit as a payment option

Hi all. Please help with a following. In Opencart presents function that allows users to have a personal account and pay from it. This applies in a firstplace. Is there any module or solution to allow user to choose to use this credit at anytime he/she wants? Please help.

Store credit is automatically applied at cart/checkout (assuming you have the Store Credit Order Total extension enabled) and there is an extension that allows you to buy store credit.

Store credit as an actual payment method is another matter, I don't think anything like that currently exists.