Is it possible to add to the eight citation styles available as a user of your online service rather than an administrator of Fidus on a server?.
Worked it out. Apologies.
For others looking for an answer to the same question:
You can create a document template. As part of the document template, you can enable other citation styles. We are using the same engine that Zotero is using for printing out the citations, so you can go here and browse through existing citation styles to find one that suits you: https://www.zotero.org/styles