2 disc brakes on one leaver

I've seen a loads of brake leavers for sale that have a double nut in place that allow you to hook up two mechanical cable v-brake/disc brake to one leaver. One such example here for anyone not in the know:

I've yet to find a double hydraulic brake leaver though. Are they the same design as mechanical ones, or do the cables meet and join before they connect to the leaver? Anybody sell these off the shelf? 

Would regular MTB hydraulic calipers be up to this task or would the pistons inside need to be bigger for it to work?

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