Move content to a temp directory before allowing playback



I have a Raspberry Pi 3 Model B with a 16GB, Class 10 micro-SD card inserted into it that is my Plex Media Server. When I only had a few pieces of content I would store them on the microSD but now my library has grown bigger, I have recently moved to a external HDD connected by Usb 2.0. It is capable of reaching read speeds of around 100 mb when connected to Usb 3.0. Although, usb 2.0 is very slow and there are large hiccups, I wanted to know if there is a way to move the content to a temporary location onto the microSD filesystem as I have tested the difference between microSD's hiccups and the HDD and the microSD works flawlessly.

A basic run down: Plex copies the content (say for example a TV show episode) to the microSD in a temporary location -> Plex plays back using the content in the temporary directory.

I am okay with any waiting times while the file copies.

Thank you!