Hovering the mouse over the horizontal scroll bar is not a good solution, if you have to move the mouse down there, then you might as well click and drag the scroll bar anyways. If you look at most programs that have horizontal scroll bars (firefox for example), the arrow keys on the keyboard allow you to scroll horizontally. That way, at least mice that have extra buttons or a horizontal+vertical scroll wheel can scroll horizontally by remapping buttons. With all the scrolling that is necessary in labview, a better way to scroll horizontally is an obvious thing to improve. (even if you make it two obscure buttons like the F# buttons, it can at least be remapped by the techies among us).
even regular windows explorer folders allow you to scroll horizontally using the arrow keys or the mouse's left/right scroll functionality if you have it.