How do I select the attack angle when using a skulljack?

I can choose which direction to use the Ranger's Slash from with the mouse, but using a skulljack activates the GUI where you can't seem to change the attack direction.

How do I choose the attack direction?

Solution 1:

As of the May 2016 patch (released at the same time as the Alien Hunters DLC), this user interface is a big better. You select the action like Skullmine, and each of the spaces around the targeted enemy from where the attack is valid (not the far side of a solid wall) will be highlighted in yellow. Left-click on one of those spaces and the soldier will run to that spot then perform the skulljack attack.

Solution 2:

In the vanilla base game, you can't.

Unfortunate as it is, you can rest easy that the automatically picked angle often is in cover, and is generally in the direction you're approaching from.