You can move cursor programmatically, andtool tip textwill get updated:
Point currentPosition = System.Windows.Forms.Cursor.Position;
System.Windows.Forms.Cursor.Position = new Point(0, 0);
System.Windows.Forms.Cursor.Position = new Point(100, 100);
System.Windows.Forms.Cursor.Position = currentPosition;
I move cursor to (0, 0) and then to(100, 100) to make sure that this trick works when toolstrip button is in upper left corner and current cursor position is close to (0, 0).
-- Vladimir