You might be able to use an overlay chart to display this data. Overlays give you the option of showing 2 separate axes (one on the left, one on the right) that are independent of each other, so in your example, your device count axis would scale up from 0 to 5000, and your device per headcount axis would go from 0 to 0.5.
The one thing to keep in mind if you do use this though, is that overlays use a combination of bar charts and line charts to display the data. This can potentially lead to a bit of confusion since we tend to think of line charts as representing trends over time. But with a little bit of user training so that everyone understands this caveat, you should be able to overcome this.