If I like the basic functionality of the setup, I may look into the available hydraulic versions on the market.I made a cable actuated left hand rear brake for my kids crf50 mini supermoto very similar to the pics you shared which is also the same ide as the OX . It works fine but not as good as the hydraulic tap.
How would you plumb the setup on the Hypermotard with two brembo masters, levers, and reservoirs on the bars?A raidal/semi radial master cylinder will fit far better than an axial one with the resviour cast into it. I made a hydraulic thumb rear brake and it was very difficult to get used to. I had an old axial master at one point and it made everything not fit nicely then switched to a Yamaha r1/r6 brembo semi radial 16mm master and it worked great ok. Then used a beringer 17mm master then ultimately ended with a megura 13mm master. That had the best power and feel while being able to squeeze it all on the bars.
Great advice, thank you. Took me a while to understand all the issues involved, but I think I got it now.Those are the taps I mentioned in my first response. I made a bunch of these years ago. Your line will need to be long(they all are for this application). 13mm is the ideal size master. As I stated before I tried 16, 13, 17 etc and 13 is the sweet spot. Megura hc1 in a 13mm is the norm for this. They are about $200 new. The HC1 is designed to be used on the left as a hand brake. It is also radial design so you will be able to fit it all on the bars easier. The $60 "kit"is usually just the tap and seal from this site. You need to buy the line and master cylinder.