I dunno.. 5-10% of outstanding btc might not be "temporary price drama".
Lets say hypothetically there is a split, and BU gets vast majority of hashrate, and BU price is around $1000. Then Satoshi would control roughly $800 million to $1.6 billion worth of bitcoin. Lets say he had very strong reasons to dislike BU, and also felt that in a free market, anybody should be able to sell their coins whenever they want. I don't know what the total order book liquidity across all the exchanges would be for BU, but I doubt it could withstand the epic tsunami of one billion dollars worth of Satoshi's BU coins raining down upon them.
I know one person, who is a long time Bitcoiner, who has the capability to do something like that. He is also rumored to be the guy who hacked the DAO. He is kind of an eccentric but he is very smart. I am scared to mention his name in public and I do not know if I should. But I would happily give it to you through pm.