The vertical/horizontal line marker has enough display options to support what you need, I believe.
In the above example, I've used a line marker three different ways; you'll want to review the options and pick the one that works the best for you. Keep in mind that you can also use hidden data series for placement.
"V,990066,0,0,5:20,-1" - line marker is 20 pixels long, but the -1 draws it below the bar so only 10 pixels are shown
"V,990066,0,1,5:20,1" - line marker is 20 pixels long and showing atop the bar (not what you want)
"V,990066,0,2,5:20,1,:10" - line marker is 20 pixels long and given a 10 pixel offset