variable blog prefix

I am in the process of creating a subdirectory multisite website. I know when doing this /blog/ gets placed as the blog prefix with this set up and I know their are plugins that remove this or allow you to change it. But I am interested in something that would allow me to have different options for different sites.

For example lets say the site is for writers and each writer will create their own sub-site. When they set up the site they get a dropdown for what genre they write in. Whatever they choose I would like to become the blog prefix for their site.

Is something like this possible. Below is the structure that I am trying to create, where johndoe and janedoe are the sites and fiction and mystery are the blog prefixes.

awesomeauthorsite.com/fiction/johndoe/
awesomeauthorsite.com/mystery/janedoe/