p2pool's sharechain already implement this mechanism. The only difference here is that each participant has a different view of what others have worked on because there isn't a reference of valid work to check (the sharechain). If someone is joining your distributed pool, they know nothing about the others and won't reward them with the expected amount so be rejected. The same problem will happen when a miner is temporarily down.
So you want miners in your distributed pool to have a way of sharing a known set of valid work (the very same for all participants unless you want to allow cheaters on board) to base their distribution on. The sharechain in p2pool does that, what's your solution?
This is won't be a pool... I'm pretty sure I already explained this. This is an idea for a protocol that will blur the needlessly strict pool boundaries. Let me give an example that should illustrate this. With this protocol, you can be cooperatively mining with miners A and B who do not cooperate with each other. This will still work.
Yes, p2pool's sharechain does in effect do the thing I'm proposing here. However, it also does things that are not really needed in my opinion. P2Pool uses the sharechain is to synchronize the coinbase transactions for every miner mining on P2Pool. For this, it uses a payment method called PPLNS. The protocol I'm describing here does not need a payment method.
The idea of a centralized valid work is completely done away with. Any share that had a coinbase that would've paid me if it had been a valid block serves to prove that the other miner is cooperating with me. There is no need for such strict protocols as used in P2Pool.