Your choice of hand brake design really is dependent on whether you want the hand brake to completely replace or just supplement the toe brakes. Obviously it's a lot easier from a plumbing perspective to have the hand brake act as a stand-alone braking system and remove the toe brakes.
If we look at it logically, if we can have brakes on two sets of rudder pedals, there's no reason we can't add another set of brake master cylinders to be used by the hand.
Several years ago there was a wonderful fellow in Texas, Jim Newman, who built a Glastar. Jim didn't have full use of his legs and as a result he built hand brakes into the airplane. He commented that most people who flew with him were fearful of the hand brakes until they had taxied the airplane for a few hundred yards, then they seemed to get comfortable with the set up, and after that it simply wasn't an issue. For anybody who has operated a bulldozer, skid-steer loader or zero-turn lawnmower, using hand brakes would be pretty much second nature.
The Glastar has a center tunnel and Jim mounted the hand brake master cylinders vertically, if I recall, with a lever system which replicated the geometry of the rudder pedals, but with longer vertical levers to compensate for our lack of hand/arm strength as compared to our strength/ability to press toe brakes.
Good luck with your modification project!