Tried it and it can not be done. It would be a disaster for all the bounty hunter who spams this forum a lot if that can happens, even for a short time, because there are many people who really want this forum to be clean form that thing.
The button only shows up for the person who started the thread. If bounty managers wanted to keep their thread clean, they would have made it self-moderated in the first place. And they won't do that, because their thread would disappear from the first page in about 4 minutes.
Bounty threads can only go without spam if all bounty managers keep their threads clean, and that won't happen as long as they can get away with spamming the forum.