So I couldn't stop myself. About ten feet of copper wire and a set of twelve aluminum "tumblers" that have been gathering dust have
been put to functional use. Wrap the wire around the tumbler about an inch from the top, twist the wire to form a loop of proper size. (the tumblers are tapered, like a Pint glass?) loop the wire under the center rad. section (adjusting for length) wrap and twist the wire end around the run and lower into position.
I used four on the 6' Living Room radiator, three in the kitchen, one in the front hall and two each in the dining room.
Twelve 16 oz. tumblers were filled on Sunday. Today they were 3/4 empty. That's over a gallon of water that wasn't in the air before.
I still have the 5 gallon humidifier, with humidistat, filled and running, but it has shut off intermittently which it hadn't before.
Due to the set back thermostat, the heat in usually only on about 4 hrs. a day. If your radiators stay hot longer, you would get even more moisture.
(But you'd have to refill more often too.)
Just about any metal, glass or ceramic container of the right size/shape could be fitted in the same way. If you "use" your radiators or if it is in a high traffic area,
you could devise something slimmer? You could even use urn shaped glass vases too for more storage volume. Just use a heavier gauge wire.
My wife is thrilled with the red/green/gold/silver cups in the living room. Very Christmassy.