variable regen / brake

Hello ,
do we already have variable regen brakes available on the market or still need to do DIY or use a second throttle?
By saying brakes I mean something like: Tektro, Magura, Shimano etc.

Where do you get variable regen sensor for yours project?
Example of DIY variable regen brake:

I couldn't seem to find an off-the-shelf variable regen brake, so I made one. I ordered some linear hall sensors on ebay (SS49E). I epoxied one of these sensors in an old brake lever housing and glued a magnet to the brake lever so that the magnet gets pulled away from the sensor when you pull the brake lever. Since I don't have a mechanical rear brake, this lever is only used for variable regen braking.

It works alright. The signal it produces varies between ~0.9 to 1.5V or so, which is just enough range for my use.