There is a way to do that, in case you don't use the model's head. Each model has a bone_head or bone_turret. Bone_Head is the one that the trigger action you posted is referring to. If you only intend to go for the arm, you can rename the head's bone to something random and find which bone is connected to the arm; then, rename that bone as bone_head. All you need afterwards is a realistic way of moving a dummy unit upwards, where the unit that has "that" arm should look at.
You will need MDLX to make these changes and Warcraft III Model Editor to find the appropriate bone for the arm (most models have a proper naming of bones, so it shouldn't be confusing); the edits will be performed through Notepad. Both programs mentioned are in our Tools' section, under the Modelling category.
Since it can be a bit unpredictable, if it is not done properly, I'd highly recommend you requested an animation for that (probably a stand - alternate).