I don't, my guess is you'd need scripting to avoid manual work.

Alt text isn't added to the image itself, it's added to whatever contains or surrounds the image—just like the image's filename isn't part of the graphic material. So it makes sense that each app will have their own way of adding metadata like alt text.

If I understand what you're doing, you can save some work by adding the alt text in your website code, rather than in ON.

Mouseover an image on your site—if you see the alt text, you're good.