I personally think a cotton ball would be too much scent.. When I don't have commercial lute, I put a drop on a Que tip and rub around the inside rim of the hive gently.. I dispose of the Que tip, but I have heard of some that leave them laying on the top bars.
Normally I use commercial swarm lure, with just a small rub of Que tip/ lemon grass inside above the entrance..
The commercial pheromone is in a small plastic vial, inside an envelope.. the bees can smell it, and are drawn to it without opening it. Scent is one of their major senses, like our eyes are to us, so I try not to overdo it.