II. Shift Draw
The idea is similar to Shift-Click moving, but instead of multiple clicks the player holds the left mouse button, then when moved, cursor will draw a path on the terrain. The ordered unit will then follow whatever the player drew on the ground once released. For example, the outline of a cliff or range of SiegeTanks.
Can also apply to Shift-Attack move. For for ranged units, the ordered unit will follow the path the player drew and attack anything within its range. For melee, it can stray outside a limited area of the drawn line to attack.
After following the line, the unit will do the next command.
Another variation would be if the player draws a loop, the units would follow the loop indefinitely unitil oredered otherwise. Sort of a twist to patrol.
This can be balanced by limiting the length of the line that may be drawn.
Specifically I and II mixed together may yield powerful results.