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
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Drieschel
LibreELEC-S802.M8.arm-7.0.2-2-devel
Booted LE With Error Mount/Dev
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Demetris
LibreELEC-S802.M8.arm-8.0.RC4
Corrupt System/Repair Failed after Waiting 2 Minutes repair failed
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The content cannot be displayed because it is no longer available.
The content cannot be displayed because it is no longer available.
The content cannot be displayed because it is no longer available.