Probably not necessary. Wort needs O2 in order to provide the yeasts with proper respiration during the rapid cell division that occurs during initial fermentation. They'll burn through most of the O2 by three days into fermentation or so. Just seal it up once the boil dies down after flameout. If you have a gasketed lid for your boil pot, so much the better. Sanitize it and stick it over the pot.