I am not to familiar with CCME but if you are allowed to configure Dial-peers on the router that is how you would 'connect' the router to the PBX.
dial-peer voice 999 voip
destination-pattern <dialed string>
session-target ipv4:XX.XX.XX.XX
"For every complex problem, there is a solution that is simple, neat and wrong" -- H.L. Mencken