Nice initiative.
Yes Ypool use 6-chain or more as shares, and each length have a different share value I guess.
I don't know how it is balanced.
Something like P2Pool might be hard to do on Primecoin (https://en.bitcoin.it/wiki/P2Pool)
Since you want multiple client/server, we will have to write a protocol first !
I guess you submit the client with some already made block hash, so that he can't go solo mining if he found a block.
Then the client return the different chain he found.
Client can ask for another batch of block to test.
I guess the problem is high load on the server (from hash generation, and chain checking)
Chain check can be done by other client though.