Don't say anything but buy one of those auto delivery room fresheners (set for every 10 minutes) and hook it up on top of their monitor pointed right at them - that should just about do the trick but if they don't get the hint, at least the room will be easier to be in with them there
http://www.samsclub.com/sams/shop/product.jsp?productId=151727&pid=CSE_Froogle&ci_sr c=14110944&ci_sku=151814