Unfortunately, despite the plethora of options available to customize Cairo-dock, the ability to turn off application switching with the scollbar is not one of them. It seems that there's no way to turn it off because it's considered a basic feature (see the description of Cairo-Dock's taskbar on this page), one that is found in other desktop environments as well (e.g. Unity works the same way if the applications are open on the same workspace).
To remove the functionality you will have to recompile the source, as explained in an answer on the Cairo-Dock forums. User matttbe provided a links on how to recompile Cairo-Dock (and specifically how to do so in Ubuntu) and stated that to disable all actions that will occur after scrolling on an icon remove these lines below from the
src/cairo-dock.c source file: