Reverse center pull cantilever brakes (how to set up and issues) Questions

Q1. For rear cantilever brakes, are there any off-the-shelf parts or brake designs that route a rear brake cable from underneath the saddle cable instead of above?

Q2. If not, then can anyone suggest an improvised, but proven setup using existing, readily-available parts?

Q3. What concerns should I have with a reverse-pull cantilever brake setup (e.g. safety, maintenance)?

Background

I have a mixte frame with standard rear cantilever brake bosses on the seat stays, with standard cantilever brakes such as these:



Since the frame is a mixte, the rear brakes are higher than the "top tube" of the mixte, along which runs my rear brake cable.  

I've seen that some mixtes use a reverse cable attachment to side-pull caliper brakes so that the cable makes a single arc from the top tube to the brakes. 
My goal is to roughly mimic this cable routing, but with cantilever brakes instead.  Here is an example (but mine does not have a rack to work around):



The original build is pictured below (not the actual bike, but same model, etc.) and has the rear brake cable running along the "top tube", curving along the back of the seat tube, and then going over a pulley that is attached to the seat tube clamp bolt.  That pulley acts as a housing stop and so it's a center-pull from the top.  I am looking to improve the rear brake responsiveness, put less stress and wear on the cable, and have fun engineering a more elegant solution.
You can't do this with traditional cantilever brakes, because the straddle wire has to be pulled from above to tension it - attempting to pull it from below would pull into the wheel.

You could pull from the side by using direct pull cantlievers, a.k.a. v-brakes. A Problem Solvers "Travel Agent" could probably be hacked up to work, and a clean implementation could probably be done with one of the no-longer-produced World Class "V-Daptor" adapters, if you could find one.

That said, both of those approaches are probably less elegant than the already-existing pulley method that it sounds like already works on the frame.