Honestly, my idea is very similar to InternetJanitor's: using a custom function (by writing your own "on thing do" event handler and and then being able to use thing[] in your scripts to make it happen when you want it to) to make things match on different cards when you move between them. IJ's idea is simpler in some ways because it checks what's currently overlapping the area and makes sure those exact things are present when you go to the next card.
There are a few things that could be confusing about either method, but I'm happy to help answer questions either way!