You can Use the TWRP from MI8 and then you only have to edit the updater script in the custom.rom.zip
0. Use "MI8 TWRP" on "MI8 Explorer Edition" and install custom ROM
1. open downloaded custom "rom.zip"
2. go to -> \xiaomi.eu_multi_MI8Explorer_V10.0.4.0.OEHCNFH_v10-8.1.zip\META-INF\com\google\android\
3. edit -> updater-script
4. change -> getprop("ro.product.device") == "ursa" to getprop("ro.product.device") == "dipper"
5. enjoy