I'm not speaking about pre-sold etchant in form of vapor. A normal inkjet printer prints by rapidly boiling tiny amounts of ink so the ink vapor gets ejected at high speed at the paper. I see no problem with doing the same to the etchant? Sure the copper doesn't absorb liquids as well as printer paper does (just print on a laser/xero transparency with inkjet printer and see how important the absorption is) but still, remove the board by holding it by edges, then wash with water. The used up, cooled etchant remaining on the surface should be much weaker.