A set of V-type sharpeners (Sharpmaker, Crock Sticks, Beaver Teeth, etc.) will let you sharpen a reverse curve with about the same ease as a straight edge. You simply draw the knife down each side while holding it perpendicular to the base and pulling it slightly towards you to reach the whole edge. Just as you would "rock" the knife as you reach the point, you can alo rock it slightly to maintain a constant bevel as it passes through the reverse-curve portion. I've sharpened Brend Talon IIs, my AFCK (which has been reground to a more pronounced reverse curve), and several of my own reverse curve knives in this fashion with great success. If you don't have a set of such sharpeners, you might consider picking one up - they are a very fast and easy way to sharpen any blade shape while keeping a very constant bevel.
(Why else would a bear want a pocket?)