Custom recording of name pronunciation when you leave a voicemail for another user

When you call to leave a voicemail for another user, and listen to the message on your Polycom desk phone, it announces who the voicemail is from using a computer generated computer. I've been told there is no way to currently change this. We've done a custom recording for the "Record User Name" function in the users profile, but this doesn't affect the name announced when leaving a voicemail.