Quoting Sabby M.
I meant the 1x4 tiles underneath the 2x4 tiles. could they be plates instead so that you could hold 2 2x2 plates on instead of 2x4 tiles? holy cow this sounds so confusing.
Ill have to try it for you, the 2x4 plate is what keeps this structure so strong. I think if you were to change it to 2 2x2 Tiles the reinforcing of the structure would no longer be connected. Follow these images but swap out the 2x4 Tile for 2 2x2 Tiles and let me know how you get on :) I could enhance this technique to allow what you want - which would allow you to checker the steps, might have a cool effect.