I like the idea of the coin. Using hashing power to generate $$ to help causes is a good idea (and being done by other projects, blazecoin comes to mind). Maybe instead of the large premie and the fact that it is being in the possession of the devs maybe you could work with one of the exchanges to have any premie (lower %) sent to them and put in a slice of each block sent to the exchange.
This way you have full transparency as the exchange would have full tracking of the coins in and out. People could easily donate their coins by using an on exchange transfer and if the exchange deals in Fiat they could actually facilitate the exchange of the crypto to fiat for whoever is receiving the donation. Maybe they would even cut some of the fees if the $$ was going to a non profit as they could claim a biz tax deduction.
This could also help keep the network healthy as the constant mining to get the block percentages would continue and there would transparency about the timining of the donation exchanges so that it doesn't look like a dump that may crush the price each time. It could also provide a trading opportunity, much like a stock before/after earnings.
Just my 2cents..
Good luck