JohnSnow
Hero
Feinting Trick has no range limitation. So the thief can stay 10 squares away from his target and still gain a bonus to damage.
It's basically Shot On The Run.
Which also makes it a good adjunct for a ranged rogue to have in addition to Ambush Trick. So you can use the latter to get combat advantage on an opponent within 5 squares of you, or use the former to get a damage bonus against an opponent at any distance.
I'll reiterate that Feinting Trick doesn't actually say you don't get combat advantage on your next damage roll this turn - it just says that you get your CHA bonus on the next damage roll where you lack CA. Which means it's usable in both ranged and melee combat.
Fascinating.