Yup this is where I was talking about Proof of proof of stake (pun intended.) For example you could perhaps make a contract where you first staked then off the stake and then back again showing just exactly how much you are staking in the period. But I am not sure that would work either if the address is compleatly different between the first staking operation and 2nd. And you would also pay twice the stake cost (albeit a minimum cost.) For sure if the pool can just set the staking pool profit margin that is way easier.
And thanks very much for the link! Appreciate it 
Edit your link also answers the questions on a contract. Staking pool can set margin so no need for a redistribution smart contract (p.34) 
Thanks again for the link.