I think you are overkilling in this one. Nobody is going to hack your private blockchain because it is not yet known and it takes a lot of time to promote and advertise it. You still have to earn the privilege of being 51%-attacked. And if it happens , it is going to be an awesome advertising for it.
Now, if 51% attack happens to your net, it is not as serious as everybody thinks. The money is going to stay there, they can't just create coins out of nothing. The hackers will make the currency unusable. So what? This happened to thousands of DDOSed websites that stayed unusable for weeks. You are not alone in this. To manage the 51% attack just increase the number of confirmations, to 1,000, 10,000 or whatever block numbers, and that is how you deal with it. At some point the attackers will leave, because it costs money to do computations.
I think that for your new blockchain to be 51%-attacked, it is a very low probability. Because to be attacked , your currency has to be accepted widely at the exchanges. If nobody knows it yet, nobody will buy the doublespent coins at the exchange. Second, the attackers need to mine a good amount of coins before the attack, otherwise it is not going to worth it to do large amount of computation for little profit. Since your blockchain is new, there are not many miners yet, so no one is going to be interested in 51%-attacking you at the time you announce it. Think like a hacker and you will understand what I mean. Would you 51%-attack DogeCoin for example ?
To prevent 51% attack I suggest you to run mining pools. Release some code that could be used by your miners if they want to setup one. This way small miners can join together and you will gain hashing power quickly.
Before going live, just create a blockchain long enough, like 50,000 blocks or so, and that's it. Don't be afraid to go live.