You could do it, without a script, by using the
Personalized Statusses in Plus!.
Though this also requires that you at least set a
name tag or a
personal message or an
auto-responder message.
But there is a trick here...
If you set the command
/away as the
auto-responder message, you actually send nothing to the chat window as an auto-response when someone messages you... That is: you actually set your status to away, but since it is already away, nothing will happen!
Bottom line:
this can perfectly be done by using the Personalized Status feature in Plus!, like so:
Plus! > Preferences & Options > Customize! > Personalized Status > Add...
And then something like this: