Allow portals in lines and shapes to be defined by end points

Right now, when you resize a portal by moving an end point, the opposing end point also moves in order to keep the center of the portal fixed. Basically, portals are defined by a center point and a width. I would like the option of being able to define a portal by its two end points directly. Basically, the two end points would be independent of each other and could be moved without impacting the other. This would make it much, much easier to line up portals in complicated shapes, like those representing cave walls.