[whysoserious]

 

EDIT: I screwed up with the 1st iteration of this post. Run is the "persistent" USB install, Live is non-persistent. My apologies for any confusion this may have caused.

No need to install to a second USB thumbdrive, what works for me is:

1. Bootup LibreELEC USB thumbdrive created with the  “LibreELEC USB-SD Creator” app from the LibreELEC website.
2. After booting I am presented with a menu with 3 choices: Install, Run, or Live. 
- Install installs LE on the hardrive of the HTPC, wiping out any existing OS's and files.
- Run installs LE onto the same USB thumbdrive in a "persistent" state, and saves changes such as libraries and add-ons. Additionally, it makes the USB thumbdrive boot to the "Live" condition by default from then on. On a USB 3.0 device in a USB 3.0 port it is as fast as a native installation.
- Live runs LE from the USB thumbdrive but I don't think it is persistent, doesn't save any changes you make, libraries, add-ons, etc.
This method uses the HTPC's ram and hardware, but doesn't make any changes to the device's hard drive.

This is how I have a bootable installation of LE 9.2 Leia to fall back on if my LE Matrix Alpha 1 installation on the internal hard drive breaks during frequent updates.