Any idea how I can incorporate that and give them the opportunity to do so? I see the Order of the Rack featuring quite a bit (we're in the second book) but the player has really put an effort into that bit of their characters backstory and I'd like to give them the opportunity.
It makes sense for the Order of the Rack to be featured as one of the evil iconic characters for this campaign, Linxia Benzerki, is featured. Alas, I haven't purchased the books as I am a player in the campaign but if you haven't looked into it, I would highly recommend the Pathfinder supplement, Path of the Hellknight. It provided a lot of good information about the orders and background information that might inspire some good ideas.
Good luck!