It seems technically impossible that a noun could follow "very", except of course for a noun masquerading as an adjective as they do in slang (boss), or a made-up noun-adjective (squirrel-like). "Hollow" can be both a noun and adjective, but it could not be understood in the sentence to be a noun.
I'm pretty sure there's no "normal" way to fill in the blanks. Only slang or something silly comes to mind.
"Boys are very ____ and must be gentlemen at all times."
Solves two of your problems. I myself would like to see a noun immediately follow "very".