Este hack deve funcionar para você.
Edit the PATH below or inside the attached .reg file to match the path to where you have MultiCommander.exe
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\Drive\shell]
@="MultiCommander"
[HKEY_CLASSES_ROOT\Drive\shell\MultiCommander]
@="Open in MultiCommander"
[HKEY_CLASSES_ROOT\Drive\shell\MultiCommander\command]
@="\"C:\Program Files\MultiCommander\MultiCommander.exe\" /OPEN %1"
[HKEY_CLASSES_ROOT\Directory\shell]
@="MultiCommander"
[HKEY_CLASSES_ROOT\Directory\shell\MultiCommander]
@="Open in MultiCommander"
[HKEY_CLASSES_ROOT\Directory\shell\MultiCommander\command]
@="\"C:\Program Files\MultiCommander\MultiCommander.exe\" /OPEN %1"