You should probably house rule it... but you get enormus synergy bonuses from Bluff already. Intimidate, Disguise and Diplomacy, right? Did I leave anything out?
It's especially potent compared to the synergy bonus of, say... Hide? Where you say, "Yay! 5 ranks in Hide. What do I get as my bonus?" and your DM says, "I'd give you a bonus, but I can't see you."