As I understand a pit adapter, that is an elbow type of device that allows the water to exit below the frost line, but also allows removal of the pump without the need to dig outside of the borehole; I don’t want anything that makes it easy, but it has given me an idea.
Although it would be a severe inconvenience in the event the pump needed repair or replacement, I was thinking of installing a four way intersection type fitting, the bottom fitting going to the pump, left side fitting water exit, right and top side fitting are plugged with a solid steel plug.
The solid steel plugs (probably best if the whole lot is made of stainless) are drilled and tapped, the plug for the side is then bolted through the borehole tube, installed in the top is a large eyebolt to accommodate the pull cable.
All buried beneath 2 meters of Earth, together with the suggestions above,, ah,, short of the cobra idea,, sorry. Then I think that just might solve the problem.