My very simple, immediately implementable solution in that other thread was drowned in a sea of complexity of merits, bumping time limits, payments, algos etc.
Here it is again.
The [ANN] topics should remain static, schemes stay listed chronologically as they are originally posted. When a user wants to see what's new, the front page will tell him at a glance.
Every new offering gets longer front page "new scheme here" exposure, bumping is nullified and users can follow threads of interest by bookmarking them. 
Cheating by duplication could be dealt with by allowing only accredited representatives of the actual scheme to start its single [ANN] thread, which would also make the OP responsible for verifying any information given in it.