Can't you just change it's style to "Footnote" ?
Record a macro by changing the style to a random part of text and then assign a button (or a combination, for example Shift+F) to that macro.
Here, maybe this will help: http://www.addictivetips.com/microso...-in-word-2010/
2007, 2010, doesn't matter. The interface should be similar enough.