Step 1:
Launch a proof of stake altcoin. For example bitcoindark clone or something
Step 2:
People mine that altcoin until the proof of work period is ended
Step 3:
People send their coins to a burn address
Step 4:
You send the new 100% pos coin to the addresses they send to the burn address with proportional to their coins.
For example i send 18324 coins to the burn address using my address i get sent back same amount i burned to the same address on the new chain
Step 5:
People import their addresses to the new chains wallet and rescan
Step 6:
You have achieved your goal
Source: This is how the Stakecoin distribution was and i got my coins and was worked good i am like it because it was like magic and stuff.
This approach works better if the coin being mined is multi-algo. 4 Algos would make it very fair, scrypt, sha256, x11(or a different GPU algo), and a CPU algo that no one has a GPU miner for.
PoW period should not end as a snapshot can be taken at any point and the new coin allocated based on those numbers. The coins don't need to be burned either.