This is sort of a variation of this thread:
http://www.mmo-champion.com/threads/...-Pet-free-spec
Except that the talent would be accessible to all. Something like:
"Lone Hunter: You deal x% increased ranged attack damage when you do not have a pet active."
For Beast Mastery maybe it could give hunters the melee spec by changing the mastery to improve melee damage, and making abilities like Kill Command and Lynx Rush performed by the hunter (ie: Hunter jumping around in a pack of mobs and swiping furiously).
Obviously this talent or glyph in question would not be mandatory and we are assuming it's balanced with the other talents to that people aren't forced into it.