If you are referring to the source object then it will be from the origin image point by default in the centre so I don't see how that can be changed, if you are using that object then you can pin another sprite to the front of it and give that the line of sight.
If you are referring to target object you can use line of sight to position object x,y minus half the width of the object, the only problem with this is you would need to alter logic depending on if its on the left or right side of the player, or above and below if that's possible. My approach is to add another image point to the front of the target object on the bounding box, you can then use line of sight to position object.imagepointx(1), object.imagepointy(1) which targets that new imagepoint and not the origin in the middle.