After a little more research and a lot of experimenting, I have it resolved.
In the JEvents Control Panel, click "Custom CSS".
Then add the following CSS Rule to the bottom of the file:
#jevents_body .month_cell_st
{
border-width: 0px 0px 2px 5px !important; /* top right bottom left */
border-style: solid !important;
}
The results can be seen at:
http://hendersonvillencvisitors.com/events