A possible alternative though is for Yvain to repost them en masse, simply redacting the few that he doesn't want around.

This seems like the best current solution to me.

The karma requirement needs the person who wants to read it to not only have the amount of Karma, but also know that the links are available to them. If he uses a non-automated method, Yvain also has to take the effort to respond to every request as well.