Combining Stacked Bar Graph with Scatter Graph

I'm trying to build a timeline graph showing certain "stage gate" dates for each project.

Each project has a start and end date (and obviously duration) which is depicted by the stacked bar chart. I can set this part up..

The problem i then have is trying to depict the stage gates for each of the projects. Ideally along project there will just be a marker for each stage gate.. At the moment i've tried converting the stage gate data series (scope, evaluate, design, build) to scatter plots but it seems to plot it on the secondary axis.. which obviously means that it doesn't line up with my stacked bar, and ultimately doesn't look pretty.

Been going around in circles for a while and just can't seem to set it up.

Any help is greatly appreciated!

PM Graph mock.xlsx

bumpity bump