I don't understand all the concern
There is no different "hose length" requirement than if the rig were four wheel.
The sulky has two bolts on the hoop frame that appear perfect for a hitch mount.
Skip the double triple articulated gizmo (though that is a great solution) , just run a pintle hitch. They provide plenty of motion for any practical purpose.
One question, Are the drive wheels on the mower chassis, independent? Or does the sulky do all the steering? Not that it really matters. But if the sulky does the steering without any power assist, dragging a trailer will take a lot of upper body strength to make sharp or quick turns.