Recently saw one of the mechs at the aerodrome pull a 152 with one hand about halfway between hub and tip, and I suppose that guy knows what he's doing. Still, personally, anything other than both hands right at the hub makes me cringe (and I fail to see the point, grabbing the prop further out makes the task no easier and just puts additional stress on the prop and other structures, even if not outright harmful).
BTW, I am no physicist or technician, but I imagine that if all the thrust force generated by the prop in flight (especially during takeoff and climb) was brought to bear at the tip(s), props would be somewhat short-lived.