The problem is that most reach weapons are too large and awkward to use finesse, and do much of their damage for leverage. Finesse weapons are also piercing, and other than a pike(Long Spear), there aren't any reach weapons that are piercing. But if you want to make one, drop the damage one die, and increase the crit range by 1 (After converting it to an X2 dmg crit).
Example:
Rapier on a Stick: 2 Handed Finessable Reach Weapon (Exotic)
Cost: 50 GP
WT: 7 Lbs
DMG (Small/Med): 1d6 / 1d8
Crit: 18-20 x2
Type: Piercing
You may want to rename that, though I find the image humorous.