Idea for the "Your posts" sectionFollow

People have been asking about e-mail notification of new posts again, and I know that was rejected as being a bandwidth hog, but I had an idea. How hard would it be to add a flag to the posts in the "your posts" section for threads you have replied to? Basically just reading the same values that the Thread view pages use to display the flags there? I don't know how much excess load that would generate, so feel free to shoot this down early if it isn't feasable. Would be cool though if it could work.