Creating dynamic tooltip for dynamic text

I’ve been working on a proof of concept and have run into a stumper. What I am trying to do is add tooltips dynamically to dynamic text. Here is what I have so far,

Type in some text including the magic word “dolor” and hit the orange button. Flash will highlight the first instance of dolor wherever it might be in your text. Groovy.

Now I am trying to figure out a way to get the coordinates of the first and last character so I can attach a movie clip covering that area that will invoke a tooltip popup upon rollover. Any ideas?