Oh but it is...

If you make an attribute for the product w/ no options, you can still specify any option using the cart link if it's just going to be a number like this. And then of course you can still go right to the cart page.

You just need to know the attribute ID for the image code, which can be generated for you in a system message by turning on the cart links module, making sure in its settings that the first checkbox is checked, and then going to the product page and clicking the add to cart button. Go ahead and put a value in the textfield and submit to see what the path is going to be for a link w/ the image code filled in, too.