It would be nearly identical to the existing OHLC demo in the GitHub examples directory. Only instead of calling .stream on the data source every time the callback is run, you would sometimes use .stream (as is there now) and other times use the new .patch method to update the date values for just the last bar. As an example you might add a bar with .stream once for every 20 updates, and the other 19 times use .patch to update the existing last bar.