This is was I used in the past:
- ring group is configured as a destination for the incoming route (local DID);
- in the ring group: Mode - Change External CID Configuration = default;
- there is an outbound route for the foreign cell number with the number of trunks configured
- in the trunk configuration: CID Options = Allow Any CID
Then for the locally originated calls I had to specify the desired caller id in the "Fixed CID Value:" in Follow Me configuration for the given extension.