APPLY only ONE payment method to a single product

[mascarp]

Hello, I need to know how can I do to use only one payment method to a single product in my virtuemart.

I mean, I have some products that I sell giving two payment options to customers but I need to assign only one payment method (credti card) to others articles that I deliver in digital download way.

How can I do it? There are no parameters in the single configuraton panel of the products to set up and choose only one payment method, can you tell me if exist some plugins to edit the core of virtuemart or other solutions to change the regular php code?

Thanks, Massimo