This is just an idea. try to spark some creativity in this forum.
You can not do it without centralized pools etc.
Beside spreadcoin similar idea was used before on minerals. What happened to it?
Big farms/ASICs?
Hashing power of each worker and/or IP will be limited to not more than 50 MH/s (see the poll) by limiting the number of shares that a worker can send to the pool per unit of time.
https://bitcointalk.org/index.php?topic=641057.0