Side by side will not work because the supports for the cage pan and bottom grate are attached to the side panels.
Back to back might work, but you may have to find a way to fill the gap between the two cages when the back of the cage is removed. They may not be flush with each other without the back panel and there may be space between the two bottom grates and cage pans that could allow gliders to escape if they are not secured together with no gaps.
You can put one on top of the other. Drop the bottom cage down to the shelf of the stand by removing the top bar support and zip tying the cage to the stand. you can then put the second cage on top upside down with both tops of the cages removed.
Secure the bottom grate of the top cage as it is not the TOP of the cage.
It would just be easier to get the Congo (Large Sturdy Cage) to get the same height all in one cage.