You won't be able to do this with the native corporate directory application. You would need to run a custom corp directory application. There may be 3rd party apps out there or you can use the SDK and build on the examples provided. Though, the example corp directory is a bit dated and is focused on pulling entries from multiple LDAPs. You can tweak it to actually pull entries from CUCM via AXL/SOAP.
So, there is an answer but it isn't very straight forward. If you are comfortable with XML and ASP scripting then it is something you can do easily.
You can find the SDK on http://developer.cisco.com/