Wix and Unbounce (custom order link)

Has anyone been able to create a custom “add to cart” URL for a Wix product?

When clicked on, the “add to cart” button on my Unbounce landing page should add the product to the Wix shopping cart. However, Wix tells me this is not possible and that I need to link the button to a product page first, which contains the buy/add to cart button.