- Separate the background light from the subject light
- Use a green background (green screen)
- Make sure the green light reflected does not spill on the subject
- In post production, select the green background
If you need to work with existing photographs with attributes you are describing, your options are what you are doing, combined with quick select tool and refine edge/refine mask.
It appears that your choices may be limited in producing the original. In that case, and if you are not already using it, I will suggest a process that may make the selection go a little quicker. If you are already using it, ignore the suggestion.
- When you select the blue channel and duplicate it, you will paint the white-ish areas as white and the subject as black
- When you pick up the paint brush to paint the border areas, change the brush blend mode (not the layer blend mode) to Overlay
- Now, when you pick up white and start painting on the background Photoshop will try to prevent the brush from painting on the dark areas
- When you pick up black and paint on the subject, the same will prevent spills into the background
- Then you can convert this alpha channel to a mask on the layer and refine it to taste, I will recommend against extracting the subject because you will leave pixels behind. With a layer mask you have more flexibility.
I did not gather from your brief explanation that you were doing this, I though I would add it here.