The only keyboards I've tuned from top to bottom have been a Rhodes Electric Piano and a Wurlitzer Electric Piano: the same principle of observing/hearing the beats applies, somewhat/sort of, although not as complicated with multiple strings per note, since those two instruments both strike the hammers against a single metallic element (one for each key) that is then passed on to an amplifier. But also more difficult in that actually reaching the physical elements are struck by the hammers is not right there in the open, like on a piano.
I'm inclined to suggest that if one can tune a stringed instrument, like a guitar,
perfectly by ear, using just a single A=440 tuning fork for a reference note, then you could probably do a piano if you can figure out the tuning hammer/wrench/whatever-it's-called, and those little dampers they use to isolate each string.
You could hook a scope, perhaps a free software one, to a microphone, I guess, but where's the fun in that?

So, based on my very limited experience, I'd say it's probably possible if you have a pretty good ear and lots of patience. And the right tool(s) and assuming your piano doesn't need to be brought up like a whole step or something.