Adding an additional fee as a payment option.

Hello,

My website www.londonstudio.co.nz/index.php/the-shop sells graphically designed templates. Where the customer picks the template online, pays, I make the customers required changes and organise the printing and delivery. Each product contains an printed imprint on it some where with my companies website on it. Free advertising right. I want the customer to be able to choose to remove this imprint as a part of the checkout process. However I would like it to automatically add say $5 to the customers bill to compensate me for the lack of advertising the same way shipping as an option is added.

• Leave imprint there (free)
• Remove imprint ($5)

It would also be nice to include a "add $5 for this months charity" that could be located in the same place.

How is the best way to set this up? - Any advice would be really appreciated.