Managing SCCM client from WSUS

Hi, 

In our customer environment recently we deployed SCCM 2012 server. However our customer want's use existing WSUS server for patching  for few machines and use SCCM only for inventory purpose.  

My question is can we use SCCM for inventory only and Is there a way to restrict SCCM clients to point to SCCM server for patching and use existing WSUS server. 

Please share your thoughts and inputs.

Regards,

Madhan