I swear to all that was mighty, that this wasn't working when I posted... now it is!

Ok, anyway, if this is the text box:

Code:
+-------------------------+
| The Assasination of     |
| Jesse James by the      |
+-------------------------+
Coward Robert Ford          <--- below the fold text
First I get the text from the last line, using bottomScrollV, and if then I can replace the last word/whitespace character with "..." and then append that to the end of the first line

In short:

PHP Code:
var LastLineText_str:String myTextField.getLineText(myTextField.bottomScrollV 1);

// this gets me "Jesse James by the " in a string
// Then just run an operation to replace "the" or the " " character with an ellipse