A pause cannot be inserted using the Translation pattern in CUCM.The alternative  is to do the manipulation on the gateway.

With MGCP there is no way you  can insert a pause. However, with H.323, you can  use the comma character in the  prefix in Dial peer configuration to insert a pause. Look for Digit Stripping  and Prefixes in the following url. 

http://www.cisco.com/en/US/docs/ios/voice/dialpeer/configuration/guide/vd_dp_feat_cfg_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1067070