Change shape of line dots on a barline chart in CCC

I'm using CCCv2 and have a barline chart, with a set of bars and 2 lines over it. I need to be able to change the shape of the line marks over the bars. I noticed there is an extension point for a line chart that does this: dot_shape. However, there seems to be no extension point for a bar chart.
Is there a way to overlay horizontal bar-shaped lines on the bars in my barline chart?

Thanks