The trick is to use a reference plane and lock the flange of the column to this reference plane.
Let me try and explain.
Put in a reference plane, say, 160 off of grid ( the trick is to PIN the reference plane in place ) and then place your column and align and lock the flange to the reference plane.

Now if you change the size of the column the flange will stay aligned and locked to the reference plane.

Pick Split Segment then select the Section Mark. you can then drag one part of the Section Mark around.

Thanks to Nick Stokes for sharing.
