Vertical line on Bar Chart

I have created a custom bar chart that shows a series of bars across the page with a timeline as the X-axis, similar to a Gantt Chart. I need to add a vertical line indicating the progress to date. Every attempt I've made adds a horizontal bar or a rectangle covering everything left of the desired line. I believe I need to change the chart type of that particular series, but I can't seem to make it work. Any help would be appreciated.