It is not hard to balance a steam system within 2-3f with air vents
such as Gorton, they have maybe 5 different ventings avalaible, it takes
time, going in each apt, monitoring temps, and changing out vents
keeping a log, but the payoff is in reduced heating costs , even temps.

Nicks boiler provided humidity adding idea is the dumbest thing you
can do, it decreases boiler efficiency dramaticaly. The last thing you
want is to constanty add cold winter water to a hot boiler. Lanlords
that know boilers spend alot of time fixing leaks and evicting idiot
tennants that want free humidity at the lanlords expense. I have evicted
a few that removed vents for humidity. Again nick your idea hurts the
lanlord, wastes gas, its not a green idea, its greed and dumb.