Here's how I did it:
in Settings, Tasks I added a "bash::ubuntu" task which I launch with :
%windir%\system32\bash.exe -cur_console:pm:/mnt
(paste it in the big box in the lower right corner)
I even set up its icon with :
-icon "%USERPROFILE%\AppData\Local\lxss\bash.ico"
(paste it in "Task parameter".)
And it works like a charm, I even set up a personnalised palette locked to bash::ubuntu (using Ap Distinct) that looks like the purple terminal from ubuntu.
BTW the latest version of ConEmu has already bash.exe setup under Bash::bash.