I'm going to toe the line on this one with a theoretical approach. Use a software based mouse driver that lets you control the mouse with your keyboard. It isn't as simple as one key press and turn around 180 deg, but may be able to accomplish what you want to do.

However, if the functionality to quickly and accurately turn 180 deg with a single key press (or event) was removed from Warcraft and instead relegated to very quick, spastic, mouse movements - perhaps we shouldn't be admitting to trying to duplicate the removed functionality.