[R-gui] Making text window follow text

I have looked through the example:
http://bioinf.wehi.edu.au/~wettenhall/RTclTkExamples/TextWindows.html

What I want to be able to do is have the textbox follow or scroll with
the text as it is inserted into the textbox. For example, if I were to
insert 100 lines of "hello", I would only see the last 20 hello's if
the textbox was 20 lines tall.

Is there some way to specify what part of the text the textbox shows? 
Or, at least a way to display only the most recent text?

Any assistance would be greatly appreciated.

Carlos Rendon