Modify Line string but keep the same z value (height)

I am trying to modify the end point of a line to a new XY position, but I want to keep the same Z value as the original vertex. Basically I want to snap the vertex onto another point but I do not want to adopt the Z value of that active point. Is there a way that this can be done using AccuDraw shortcuts or by invoking another snap/lock before accepting the new XY location?