It would take a rather large percentage of the reward pool and allocate it to that one post. I'm not sure that's the best way to go about it.
Don't forget that individual donations can be made. If some whales want to give more, they can always dip into their account wallets and send as much as they'd like. Would be great to see Steemit, Inc. do something like that. They have millions of dollars in value and it would make for an excellent PR story about the platform's utility and generosity. That's how you do marketing (and also help someone out).
RE: @abit and @smooth - Please remove your downvotes.