YOOOO I FIGURED IT OUT! Here's a print-out template for what I'm now calling the "Super Duper Card", a micro-sd card holder the size of a playing card.
I'm releasing this immediately as CC BY-SA 4.0, which means you can make any changes you want as long as you share your work and mention my name, can be in small letters on the back like I've done here! I hope you find this useful!
edit: v2 here
