I still don't know how to make the sdcard appear directly on my desktop computer when I connect my phone, but I have a workaround : symlink the sdcard mount point in the /home/phablet directory ( = "internal storage" on the desktop computer). This is easily done using the terminal (or adb shell). Find the exact mount point of the sdcard using the command mount; it is something like /media/phablet/XXXX-YYYY. Then enter ln -s /media/phablet/XXXX-YYYY ~/sdcard