charge for file download and varients of types?

So, let me explain.

As you can see on this page:
www.therollerskate.com/photos/duluth/pro...h-aerial-lift-bridge

I have three types of prints (canvas, poster, and framed) with multiple sizes.

Now I would like to add the ability to purchase a desktop background image file.

I'm wondering what the best way to accomplish this would be. Is there a way to list the file download separately from the characteristics?

I sort of answered my own question by adding a separate "product" for the image file as an option for the print. Seems like a lot of work though, still wondering if there's a better way to do this.