Hell, if I were him, I'd have deliberately blown a few thousand dollars of the budget on disinformation, hiring a few extras to come in at the end of shots dressed in Sikh turbans or green leotards and Gorn masks so that shots of those characters managed to find their way to the press.
"You own a home-made Police Box? I'll give you $800 out of my own pocket if you bring it down so I can have shots of Kirk and Spock checking it out leak to the Internet. I'll even throw in a copy of some artist's renderings of Archer's beagle as a Borg if you pinky-swear not to upload it anywhere until after the movie is released."
Remember all the Bennett-directed misinformation on TWOK? Multiple endings, Spock lives, Spock dies, Spock maybe does?
He called it throwing tin foil into the radar sets, I think. And he managed that without an internet, and for the most part, without any backlash during the theatrical release. But it only held till about a month prior to release, because The Tonight Show announced his death after the Kansas test screening.
If word hadn't leaked at that point, would crowds have been bigger or smaller? It still did what was the usual thing for TOS Trek films -- biggest opening weekend ever -- so there was curiosity beyond that initial question of Spock's survival (which seems like a much larger matter than the Cumberbatch character's identity, especially since the actor himself is at this moment in time probably more of a draw than the character name.)