Is it possible to enable "Focus follows Scrolling"? I tried out Focus follows mouse and found too many occasions when it really annoys me. Thinking about the cases when I would need focus follows mouse, I realized that it's only necessary when I'm scrolling in a non-active window. 

So: Is there the possibility of having the focus switch to a window in that I scroll? Either via some setting or external application?
I find that many applications already behave this way.  At least with a trackpad.

If I am working in this window, responding to your comment, and I hover over another Safari window, OR over my iTunes window, I can scroll without clicking on the other window.

My computer is not set to Focus follows mouse.

It may well be that some applications do not support this... 

Do you have a specific set of apps in mind?