I had a look at the your demo and also at the plugin page and I'm afraid this is going to be a bit trickier than you might think.
I don't think there is a native JS event you could use and to implement what you are asking.
Rather, you would have to examine what the plugin is doing in response to the
mousemove event and alter the code from there.
A much easier option would be to use a thumbnail scroller that supports this natively, such as this one: jQuery thumbnail scroller (kind of).
This has a
noScrollCenterSpace option, with which you can specify an area which, when hovered over, stops the scroll.