Don't want to try myself but, at least you can take a peak what I found:
http://i13.tinypic.com/5ya1ogz.jpg
(Found in the local MPQ file: "DBCFiles/LFGDungeons.dbc")
Maybe we could edit level requirements, and be able to for example LFG Deadmines as level 70... but not sure if this is doubble checked server side. Might look around but, personally can't afford testing out on Blizz server for fun. :'(