You could make a little plugin that you can turn on/off when you need it. It's been a while since I did any vbscript though but something like...
If InStr(1, InputString, "@", 1) > 0 Then
GetResponse = Replace(InputString, "@", "")
HalBrain.ReadOnlyMode = True
End If
Or something like that. the idea is that you prefix what you want Hal to say with an @ (or some other barely used symbol).
If I got the right command (Replace) it will take the input string and remove the @. Then Hal says the word or line.
User : @brrr
Hal: brrr
This is just off the top of my head, you will probably need to play with it.