I want the same thing, and... there's an alternative to that and works pretty well, explained by Mark in his answer here, using xbindkeys & wmctrl.
Just install them both packages:
sudo apt-get install xbindkeys
sudo apt-get install wmctrl
.xbindkeysrc in your home directory and put your desired programs like this:
"wmctrl -xa Nautilus || nautilus"
Alt + 1
"wmctrl -xa Chrome || google-chrome"
Alt + 2
"wmctrl -xa SublimeText2 || sublime-text-2"
Alt + 3
"wmctrl -xa Filezilla || filezilla"
Alt + 4
"wmctrl -xa Firefox || firefox"
Alt + 5
Then log off your account and login back again.
Using ALT+# open an instance of the defined program on
.xbindkeysrc, or if that app it's already running then the shortcut will focus on that app.
Sadly you have to manually put what programs you need on your
.xbindkeysrc file, but it works superb ;)