Disable error message on trying to add to cart/redirect?

Hello there. I'm working on a project where we have a simplified checkout process, where users need to only be able to buy one of a product (it's for buying access to content). We're using Commerce Cart Redirection → to streamline the checkout, so users go directly to checkout when adding to their cart. If a user somehow finds their way back to the product page when they have the product in their cart and clicks the button again, they end up with an error message and stay on the page - in this use case, it would seem like better UX to redirect them to the checkout page for the cart that they already have, but I'm not having any luck figuring out a good way to do this.

I'm only somewhat familiar with the inner workings of Commerce, but fairly experienced with Drupal core.