Support cmd voicemail "a" extension in extension configuration.

My specific application is to have a caller hit * while in cmd VoiceMail which will dial a follow-me extension for the user they are trying to reach. I have heard of many wordarounds like using a ringgroup and an IVR, but that's not a scalable solution, especially if hundreds of users want to use this feature. The cmd VoiceMail() a extension is a perfect way to accomplish this, and has worked well for me before the days when I was using FreePBX.