If you were building a CP from scratch, you could glue thinner pieces together. So for example, if you wanted a 3/4" CP with a 1/4" deep area routed out, you could use 1/4" and 1/2" thick pieces. Then you could cut out the region you wanted in the 1/4" piece, then glue it to the 1/2" piece. End result would be a 1/4" deep recessed area.