A simple Dual SD card holder I made for a friend with a notched/tab to keep it closed. Easily fits two cards - will likely work on a revision for 3-4 and maybe a micro sd insert. The spring is just enough to keep the lid from moving on it's own and enough for you to easily move it just by sliding with your thumb/finger.
We used this thing as inspiration but built ours from scratch for customization.
There's just enough gap on the springed tab to put a layer of support and have it break free when you move it. You probably won't be able to remove the support in the middle, but it still works just fine.