For the UC500 in CCA. You probably could break apart the FXO Group and then configure your outgoing dialplan with a specfic number. Under the "Begins with" column you could enter the entire number. Number of digits could be 11 if you dial 10 digits for outgoing calls. Under configure set the FXO port that you broke apart from the rest to have a priority of 1 and then add the rest of the trunks with a lower priority if the FXO port is busy.
Using CLI would be a nightmare since there already COR lists in place and its not supported.