This is not quite what you were describing, but achieves the same result ... I've used ClipMenu for years and couldn't live w/o it: http://www.clipmenu.com/
I keep a clipboard history of 75 items and also have "snippets" saved for easy pasting of commonly used phrases. You can assign a keyboard shortcut to pop up a context menu next to your cursor. Pretty handy.
Such applications are text replacement utilities to insert blocks of text into other applications by simply typing a few user defined keystrokes. Anytime a user defined keystroke combination is typed, it is substituted with the replacement text. Example: you type "email1" and that text expands to "thisismyemailaddress@hotmail.xxx".
It might not work with passwords though.