Just to double check, you are sure you have the ELIN specified as a translation pattern which directs calls to the CTI route point which points to CER?  It has been a while since I set this up but as I recall the cisco doc had a config like this:

CTI RoutePoint DN 911  (points to the primary CER server and CFNA/CFB/CFOF to 912 - if applicable)

CTI RoutePoint DN 912  (points to the secondary CER server and CFNA/CFB/CFOF to PSAP or local security/emergency personnel - depending on customer policy)

CTI RoutePoint DN 913XXXXXXXXXX (redirect PSAP return calls to CER for processing)

Sounds like egress to the PSAP is fine for you.  The problem is calls coming back from the PSAP.  So the call flow would be:

1. PSAP calls pattern.  Example: 2025551234

2. Call comes into gateway

3. Gateway hits translation with following config (for example)

Pattern: 20255512XX   (for sake of argument, let's asusme all of your ELIN's are in a contiguous block of DIDs)

Partition:  Something the gateways can see

CSS:  Something that allows the translation to see the CTI RoutePoint for CER

Translate Called: prefix 913  OR calledparty transform 91320255512XX

4. The CTI RoutePoint 913XXXXXXXXXX is hit and sends the call setup to CER

5. CER does a database lookup for active 911 calls in the target ELIN

6. CER redirects PSAP to orginal caller

This last step merits closer attention.  I am not sure if CER does a CTI route redirection.  If so, I am not sure which CSS comes into play.  I would check the CER CTI port (not route point) CSS and the gateway CSS to ensure they can reach the line of the IP phone that placed the 911 call.

HTH.

Regards,
Bill