I suggest to use the pane's setScrollPos
method and to set it to the corresponding values of top and left based on the size of the pane itself - in this manner the scrollbar should always be on the bottom. You can do this on the particular event for your case, e.g when a button for sending the comment is clicked.
Please, use this suggestions as a start point for your implementation and in case I have misunderstood you or you need further assistance, please open a support ticket and send me a sample, fully runnable demo along with detailed explanations of the actual and the desired result and I will do my best to help.
the Telerik team