Ok, so finaly I find a great solution for this case.
As I said before in a comments, the better solution is to use a script called with the Ayatana shortcut. This is an exemple of Quicklist launcher for gedit. With it you can open a file in gedit or open a file as root in gedit
The part I add in the gedit.desktop file :
[OpenDoc Shortcut Group]
[OpenDocRoot Shortcut Group]
Name=Open file as root...
Using a script fine is more easier for testing what we want and do some complex things with the quicklist shortcut.
Now this is the code for the script /path/to/the/script (personally I create a script folder in ~/.local/applications/ folder and create the script geditshortcut in it)
case $1 in
normal-mode) gedit $(zenity --title='Open file...' --file-selection);;
root-mode) gksudo -u root -m "Running Gedit as user root allow you to modify some essential files of your system" "bash -c 'gedit \$(zenity --title=\'Open file as user root...\' --file-selection)'";;
Now Drag & Drop the gedit.desktop file to the launcher bar or Unity and enjoy it ;)
That's all folks !!