Actually yep I do look for nipples I did another google search on it and everything is saying that male rats do not have nipples. I didn't go to the petstore and get full grown adults I got young rats. I'll try the dangling them off something though never thought about that with the young ones that suck it up does that still work? Oh and here is a link to a hairless male and yep no noticeable nipples, not to be sarcastic but wanted confirmation for myself.
http://media.photobucket.com/image/h...irless_rat.jpg
Maybe there is a member here that has a hairless male that can confirm if they are just so small they are not recognizable in photo though.