Nero aac enc is part of a proprietary encoder by nero, and I'm not even sure if it's available for linux anymore. I sort of doubt it. However, faac is an open source (gpl licensed) encoder and decoder of aac files. I'd be happy to help you switch by providing code from another cd ripper if you're interested, although I'm not much of a coder. If this is added, would it be possible to add support for creating .m4b audiobook files? Those are aac files wrapped up in an mp4 container, mostly used for audiobooks. Sorry for my chattiness, this is my first bug hear.
See also bug 54 for fdk-aac support.