It could be changed in a custom script. Currently, when dialing by extension the extension is simply played back while dial-by-name will play the name.
For information about that, you can check out some of the custom scripts that were with CUE 2.2.1. The example described here:
http://www.cisco.com/en/US/products/sw/voicesw/ps5520/products_tech_note09186a008041d950.shtml
has an example in the download section of one of those releases.
The idea is to look at the dial-by-name section and grab the part where it gets the user's spoken name (and checks if it exists), then put that same snippet in the dial-by-extension section.