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Hot water radiator valves need to be either all the way on or
completely off. Partially closing them does nothing.

Well, admittedly, I was thinking about steam radiators,
having keyed on "big iron", instead of FWH, but unless
the radiators in question are either hooked up serially
with no bypasses, or driven by separate pumps,
I can't see why it wouldn't work, anyway.
Are you thinking of solonoid-driven valves, which
don't really HAVE a partially closed state, or is
there something about the dynamics of a typical
HWH system that causes them to ignore flow restrictions?

--Goedjn