Hi,
I don't fully understand the problem, but will help where I can and hopefully ask the right questions to help fully grasp the issue at hand.
The part I can answer is that to make sure end users can't dial the ELIN patterns is to make sure the inbound CSS on the GW is the only CSS that can reach those ELIN translation patterns.
Now for the questions:
1) How many digits is CUCM receiving from the Telco? 4 or 10?
2) Can you provide some examples of the problem you feel you are going to face? (feel free to use some X's so you don't advertise your DIDs and DNs)