I have a client who uses fixed table rates to calculate shipping prices on his website. Behind the scenes, he ships all of his orders through UPS. He would like to automate creating shipping labels through the website, but Magento 2 only allows shipping labels to be created if the order itself is associated with UPS (or another shipping provider). So it won't allow "offline" shipping providers to use shipping labels for "online" providers.
Is it possible to enable UPS shipping labels for orders using fixed table rates to calculate the shipping price?
Existing plugins would be ideal. If not available, I'm looking for guidance to implement it myself.