I'm running Windows 7 x64 with Gvim 7.4

Using my external mouse, I was wondering how to achieve 'horizontal scroll', I read all the documentation about it but still haven't figured out how to achieve it. 'horizontal scroll' to me means holding down the middle mouse button and moving the mouse horizontally. But that's just not working. Essentially what I want to achieve is something like this VS plugin.

I know about zl/zh but I want to scroll horizontally from the mouse (by holding MMB and moving horizontally like I said, somehow, maybe?)

So when does ScrollWheelLeft/ScrollWheelRight events get fired?

Thanks.