FPS Quickscope Button
A downloadable tool for Windows
This program utilizes the clicking of the middle mouse button to immediately scope in, and then fire a half second later. (Note that this overrides the normal function of the middle-mouse click, and you must have your scope setting in game as toggle if possible)
After installation double click on the program to run the AutoHotkey script. There should be an icon at the bottom right in the taskbar.