So what you are saying is, you still only have one physical line (Line 1) going into the CICS system?
That service was called Ringmaster a few years back with Bellsouth. I never used it much, and only with fax machines and such. You have to have an external switch, similar to a fax switch. Again, Bellsouth called them Ringmaster switches.
Even with a switch like I have described in place, you would only be able to recieve calls on the 2nd number. All outbound would still go out on the single POTS in the CICS. And, without call waiting, anyone calling EITHER of the 2 numbers would get a busy.
Anyway, I understand what you are trying to do with the CICS. Distinctive ring is not gonna do the trick. Nor is there anything more that the CICS can do for you.
If the line was added for incoming traffic you could use call waiting. But, that would only allow one person to handle the calls. If a 2nd line was added so more than one person can be on the phone at the time, you will need a physical 2nd line.
Hope this helps