Hello Gaurav,
I'm afraid you need a C6500 or C7600 with Sup720 3BXL or better for this job.
I tried to look at the c4500 configuration guide and in the QoS section there is no reference to MPLS frames and EXP.
However, if your only objective is to have the CoS bits to reflect the MPLS EXP bits this can be a default behaviour being the MPLS frame the payload.
ethernet header -- 802.1Q header -- MPLS header
802.1Q CoS should be a copy of MPLS EXP bits by default when it exits the PE interface.
Hope to help
Giuseppe