I did get this to work by SDcard and am running 8.2rc1 on my MXIII-G 2g/8g.
Download Libreelec - see post on page 476 page 32 - I used the 7.0.1c link and downloaded this image -
1- Download "Enable SD card dual boot" zip file, extract & copy files to sdcard/thumb drive (I used sdcard) - OpenELEC-MX3G.arm-DualBootSD.zip
The OpenELEC-MX3G.arm-DualBootSD.zip Worked in getting this box to Boot Off SD Card. YAY!
The rest is all downhill because what i believe is a Linux File System Used on this box that will pretty much Lock Out LE
Unless i Flash Android and go again.
Results after Successful Dual Boot Script zip.
wilro
LibreELEC-MX3G.arm-7.0.1c
Black Screen
Demetris
LibreELEC-S802.M8.arm-7.95.3.001
Black Screen
Demetris
LibreELEC-S802.S82.arm-7.0.3
Booted LE With Error Mount/Dev
Drieschel
LibreELEC-S802.M8.arm-7.0.2-2-devel
Booted LE With Error Mount/Dev
forum.libreelec.tv/core/attachment/1852/
Demetris
LibreELEC-S802.M8.arm-8.0.RC4
Corrupt System/Repair Failed after Waiting 2 Minutes repair failed
forum.libreelec.tv/core/attachment/1852/forum.libreelec.tv/core/attachment/1853/forum.libreelec.tv/core/attachment/1853/forum.libreelec.tv/core/attachment/1854/