Organising audiobooks?

I want to organise my audiobooks according to those I have read and those that are currently unread on my Ipod Classic.

At the moment they only organise in alphabetical order according to Title. I have tried putting Unread into Grouping field in Itunes and tried sorting by Grouping but this doesn't affect how they appear on the Ipod. And because they are Books and not Music they do not have a Genre field which I can find on the Ipod but Grouping does not appear on the Ipod.