Single registration of two premises under central excise

dear sir

My client has two units one located opposite to each other. Unit 1 is a pvt company registered under excise while unit 2 is a  non excisable proprietary concern which is currently a job worker for unit 1 ,doing an intermediate process for unit 1. The assess wants a single registration for both of them in terms of excise notification 36/2001-c.e (n.t. ) dated 26-06-2001. I would like to know how difficult or easy this process is ? does this require the permission of the commisioner etc ?