As currently written, that behavior varies by browser or perhaps jQuery and/or jQueryUI version, so I think it may be hard to track down. If you use the:
property in your init, it looks like you will get what you want, but of course, the scrollbars will always be visible. Example:
That will initialize the Facescroll to that selector with the scrollbars always seen and then scroll it to the end.
I will look into what you're asking, that it do that even with the scrollbar hidden. I think a better way might be to have the scrollbar remain visible until drag ends. This is also tied in with behavior on touch devices though, so it might be tricky. I have no way to test on touch devices, so I've been leaving a lot of the code alone, as to not disturb that part of it.