Include a link to a member's mainsite profile by their posts

[Q-Nova]

Remember how in the phpBB era each post would have a mushroom at the bottom that would take you to the poster's main site profile, if they have one set? I'd like to see that brought back in MyBB, if that's possible! If you can't embed it with posts, then you could put the link in the profile pages. We already have a mainsite ID form in the user control panel, so why not put it into good use?