The only thing I can think of as a semi-solution is: forum members may not be paid for more than X posts per day - no matter the campaign. It would slow things down.
Another rule suggestion means going through another series of debates and another pile of work for the DTs. Don't get me wrong, I like your suggestion but the question is do they like it too?
You know what? For me, daily or weekly post quota is not a big deal. If you're really eager to complete 20 posts per day then divide it in subequal parts, if it means posting every hour for the rest of the day then do so instead of forcing yourself to complete it in several hours only. It is also good in a sense that you can have some ample time to refresh and gather new ideas/motivation thus quality of your posts are not reduced every time you post. It's just a matter of time management and discipline.
If you believe that you are not a shitposter then prove it to others,
at all times. If you can't then prepare for the consequences (ban/red tag) Lol.