I wanted a micro SD card holder for my Ender 3, that is accessible even when the bed is forward. I did not want to use the electronic box screws, as I have already a fan shroud mounted there.
The micro SD card holder is mounted with the two left front screws and double sided tape inside along a ledge. The ledge also keeps excess cable inside the holder before mounting it to the printer.
I made room to use the optional micro USB port. As this port is very close to the SD port, it was necessary with a slot in the holder, so that there room for both connectors - se pictures.

https://www.youtube.com/watch?v=UB5eMtef4BE

I used this eBay SD cable adapter:
https://www.ebay.com/itm/Micro-SD-To-TF-Card-Extension-Cable-Adapter-Flexible-Extender-Hot-Sale-US/132279236140?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
(working link as of 2020-02-16)
Link title: "Micro SD To TF Card Extension Cable Adapter Flexible Extender Hot Sale US"
Price: US $2.47
Size measured: Height x width x length= 7.2mm x 25mm x 32.8mm

Consider donating a cup of tea - or maybe even half a cup of coffee.