Panhandler - i have traveled this road and found the attached link.
Towdster In-Water Towing Device
They have several products for varying applications, i chose the one shown on the homepage link, the V version.
We have a 8kt 38 ft cruiser that does not plane.
This is a positive control system that will control the towed vessel.
I installed a redundant automatic bilge pump for my peace of mind. The dink tows about 8 ft back and i can adjust this to keep her on the back side of the wake. It works well.
I am towing a 13 ft Boston Whaler with a Yahama 30.