Display X-Axis Labels on Two Levels to Improve Readability

[PhamHall]

I'm working on a rolling 12-month chart, where the X-axis is MMM-YYYY format. The chart will be posted in 4-panel slide. So the x-axis after being scaled down in size will be hard to read. A solution would be to alternate labels between two levels. Month 1 would display just below the x-axis, Month 2 would display one row below the x-axis, Month 3 just below the x-axis, etc...etc...I've seen this done. So I know it is possible. Question is, how to do it?

Thanks,
Brian Hall