Hi,
I frequently make these sparse dot plots -- this is tracking a metric over a counting metric, so left to right is further into a test. The ordinate is a one-dimensional spatial location. When we see shapes in the data, we want to know what event may have precipitated them. What we typically do is use Color of an event column. But I'm not a fan because the colors on these small dots can be difficult to see, and not easy to track with eye since they move all around.
I prefer this method, where I attach a line to the axis ... but that means I would have to script it. That's actually where I'm at -- I don't think it would be that difficult, but thought I might be missing something.

I also tried this, where give my events is a certain space on the ordinate axis. So now I know where to look for the events:

Then there is this way, which I don't like because it devotes too much space to the lower chart and I don't seem to be able to re-size it:

Lastly, I've put the events onto a right-side axis with not-great results.
Thank you!