I have a component which has a cavity on the bottom (the side that meets the top of the PCB). 
How can I create a keep out region which spans the outline of the component, excluding the cavities?

[![Illustration of keepout][1]][1]

I tried using primitives for the outline shape and the cavities, marking them and using tools -> convert -> create region from selected primitives. 
What happened was I only got a region that spanned the entire outer layer. 

Any easy way of achieving what I want?
Thanks!


  [1]: https://i.sstatic.net/Ja4jc.png