Here are a few options:
You could assign a numeric value to each of the choices in the Rating Scale as in this FAQ:
(see my next reply for link, it wasn't working here for some reason)
You could also edit the list of choices and replace the rating (Disagree - agree) with numbers, this would change the values displayed in the web form users fill out as well, so the assinging a numeric value may be a better option.
Last (and probably least attractive) you could do a "Find and Replace" finding and replacing all instances of "Disagree" with a corresponding # and so on. Use "Ctrl+F" (Cmd+F if on Mac) while on the View Responses tab to bring up the Find and Replace feature.
I updated my previous reply, adding response to ensure email is sent...