For me the simplest solution is keeping different accounts active in different browsers. I've not cheked all the options with youtube and such, so maybe it doesnt work for youtube alias, but it seems to behave correctly so far to have several accounts open at the same time but not merged.
I'd been remaining logged into Google pseudonymously much of the time in an incognito Chrome session. I'd occasionally hop onto my other Google accounts in another Chrome session, though by preference I'd stay logged out.
Among the other benefits: simply not having to put up with the blasted Notifications icon every time I'm on a Google property.
