I see a problem here :
Even if all the miners decided to give 0% donation, you will still be able to mine with a 10% more block reward than any other miners.
And I guess if you make a pool miner you will set this to 10% and possibly you could attract all the miners in your pool by giving them 1% or more bonus from your donation.
This cry-out centralisation to me !!!
As for me now it is easier to be friendly with all pools to get donations from them, than build ours own pool.
But you right, it's a possible problem. Have any ideas how to improve this point ?