Perhaps posts by those who are not the OP can be ignored when determining thread ordering. To go a step further, the OP could designate one post per day that will “bump” the thread to the top of the board.
This should entirely remove the incentive to use fake/paid bumps.
A few months ago theymos created this thread:
Ideas for topic ordering in altcoin announcements?
He suggested an interesting idea of how to remove the incentive to use paid bumps and spam in announcement threads. Many members proposed their own ideas, but as I can see, bumping services still exist and work on the forum.