I've never tried it but I don't think DISA will let you dial access codes except for trunk access or station access.I don't know why it would, imagine the "fun" someone could have if it did.
You would also need a dedicated trunk for DISA . I assume this customer is live answering the lines? If that is the case you could use next port on the station group to the auto attendant and like mentioned you can manually set the voicemail mode.