You could try this method based on one I’ve used in the past to find the balance point of a telescope tube.
- Fit the telescope to the wedge and stand it on the floor.
- Slide pencils in from opposite sides, level with each other, effectively making a see-saw.
- Slide the wedge back and forwards on the pencils until it is in balance.
- The vertical plane through the pencils now contains the COG.
The only issue you might have is if the COG lies outside the wedge and it tips over when placed on the floor. In this case you could attach an outrigger to prevent tipping before putting the mount on the pencils. As long as it is light in weight compared to the scope it will not materially shift the COG. After all it will shift in use if you switch from say a light eyepiece to a heavy camera.
Just a thought.