I was thinking fingernail to pluck/pry it open? It depends on how tight the gap is and how strong the magnets are. Really like the idea and design, though, and hope you can find a way to keep it as clean and un-noticeable as possible.
A pull-ribbon would show. You could adhere a "mass" inside, and use momentum into an abrupt stop to pop it loose, but that means getting the "mass" just right, so it only pops when you want it to.
I got it! When you want to take it off, just put a piece of tape on it and lift!...
Cheers,