Not updating the chart while "paused" is not a viable option, because the user may later want to scroll back to see data that was collected while he was reviewing older data. I like ChrissyC87's idea of deferring panel updates, but it prevents the x & y axis scales from updating while scrolling, and the chart does a lot of funky things if you try to manipulate the scales or pan/zoom. Surprisingly (to me at least), it doesn't prevent the plot from redrawing so as to sync the data with the position of the scroll bar.
I was hoping there would be some simple property that I overlooked that could be set to prevent the chart from automatically scrolling, but that seems to not be the case. Alas.