How do you set your mouse on 5, and mouse on 4, to act as if im holding down shift or control?

Im trying to optimize my mouse, so that the extra side ons that has no current use for anything, acts as a modifyer key (shift, alt, ctl) for my world of warcraft keybinds. the mouse doesnt have any 3rd party sofware, its a usb "gear head" mouse Item no:KB5500W. Help please?