Copying directly to an SD card

Is there a way to copy video files directly to a SD card for offline viewing on a mobile device without going through the Sync feature in the Plex app? I have set up Amazon Fire tablets for my grandkids to watch movies in the car, but using the Sync feature is slow and tedious so I was hoping I could just copy the files directly onto a SD card and then bring them up in the Plex app.

The only way I can think of making this work is to download them manually and set up the device you download them to as a server.

https://forums.plex.tv/discussion/170771/plex-does-not-show-any-movie-files-on-my-sd-card

Since you asked so nicely anfrey, we only support playing your content from your DCIM folder (here).
Plex is not designed to be a standalone video player, for playing back files that you’ve copied to your local device. It is designed for playing content from your Plex Media Server. If you’re looking for a standalone video player, try out MxPlayer or VLC to name a few.