I guess you could build a launcher that would do that. Something like this:
Create a new text file with the following contents:
Code:
[Desktop Entry]
Name=Eject media
Exec=eject
Icon=(choose yourself a icon you like)
Terminal=false
Type=Application
StartupNotify=false
Name the file Eject.desktop. Right click that file, select Permissions and check Allow executing file as program. Then you can drag it to the Unity Launcher and when you'll click it, the tray will open.
Tell us if it worked, please.
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