Do you really want to do this. Personally, I use a password db which stores all my pw's with a master pw. That way I don't forget any and I don't leave my computer open to fiddling by kids and horrible people.
If you want to use it due to convenience, that's something else. There are many reasons why password fields exist. Shortcutting to effectively not having one, even on your own PC could be disasterous.
I apologise if this doesn't address your original question.
//EDIT
Almost forgot:
here's the free pass keeper: http://keepass.info/ I use.
diafol
Rhod Gilbert Fan (ardav)
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