How to change the cursor hotspot in OS X 10.8.5 Mountain Lion?
I'll give you an answer you'll hate. You would have to batch change the .png of the all OS cursors in: 

/System/Library/Frameworks/ApplicationServices.framework/Versions/A/Frameworks/HiServices.framework/Versions/A/Resources/cursors

In the neighbourhood of a 100 pngs and adjusting singular pixels is what I see as the only option because there is no other way I can think of to adjust the 'active hotspot'