make a rectangle that doesn't change with zoom.

I’m trying to make a rectangle that “highlights” a straight line of markers such that:

  1. it surrounds/contains the points, basically like:
  O                    O                   O                  O          |

  1. its height doesn’t change with zoom. (it should always be approximately a little taller than the height of the markers’ heights).

I can do (1) but so far not (2). I’m pretty sure I need to use a blended transform for this somehow…and possibly TransformedPath, but I’m lost as to how to do this.