So I’m sure you’ve probably found a new plugin, but I found a workaround to this issue. I created a Cartflow landing page that looks like the single product page with a button that is linked to the checkout page (next in the flow). Then, once the user clicks the “Checkout” button, it will automatically put that product in the checkout and so on…
Hope this helps someone because I also was very disappointed when I put in all that work to find that it didn’t link to the right checkout page when purchasing a certain product.