I don't like this idea. For 2 reasons:

1) The board members won't see immediate feedback about their posts. Also, this will slow down response time to valid posts.

2) This sounds like it requires much more upkeep than just deleting spam posts once they are found.

I prefer doing this:

A. Change the login to require the user answer a simple question to stop spambots.

B. Allow posts and user accounts to be deleted to force the manual spammers to re-create their accounts.

If the spam doesn't live long on the board, then the manual spammers will eventually give up and find another board to spam. I can monitor all posts and delete spam very quickly during business hours.