You could do something like this by going to Instant Search Administration, chaning the number of products setting to some high number, then you should go to the plugin folder -> Themes -> Your Theme -> Content -> InstantSearch.css, there you should be able to find .instantSearch .k-list-container and replace the styles with the fawoling:
When you click on anything outside of the results box it should disappear. I suppose by scroll bar you mean search results box scroll bar, it shouldn't disappear when you click on it. Which browser are you using for testing ? Which theme are you using ?