If you want to reproduce the beer, get a tube of Brett, dump it in your bottling bucket and then package. I'd bottle-condition with Brett but be advised, the residual saccaromyces in your beer will do most of the carbing so undercarbonate to give the Brett a chance. I can't say by how much, though. Maybe don't add any priming sugar, since Brett can digest some of the stuff saccaromyces can't. Do some research, I'm just throwing stuff out....

 

You wouldn't happen to have a copy of the book American Sours by Michael Tonsmiere would you? He does have a section in the book on this topic. He may even have information on his website. https://www.themadfermentationist.com/
If you're into sours and funk and the like, his book is excellent and a great read. I'd venture to say must have. Milk the funk may be a good reference for you as well.

 

First off sounds fun! But I think I would finish ferment with the Brett. It always cleans out more sugars so will over carb in a bottle maybe? The million dollar question is when In fermentation to introduce it. My guess would be with just a few points left as the sour isn't a huge stand out if I remember correctly. Keep us posted.
CHEERS AND GOOD LUCK


Edit:
By the way had a beer from Treehouse brewing a while back and it had a slight sour tart to it. Liked it so thought maybe would propagate the yeast. Did a small starter and it was very sour, not like the beer at all.
They must be doing what you are investigating

 

Pure brett primary fermentation is surprisling clean and very like a sacchromyces fermentation.

I was listening to an interview with Tonsmiere on Basic Brewing recently and he was mentioning new information on how to maximise the funky flavours from Brett. It was very much in passing but he was hearing that it may be more related to using it under pressure or for packaging.

I've done a couple of shorter mixed ferments with brett c which have had a nice slightly tropical fruit aroma from the brett. Haven't had them packaged long enough to really get a feel for how it ages though. Which sort of points to the other thing i'm hearing people with far more experience with brett say, that's it more diverse and has a wider set of flavour profiles than sach, and people are only just starting to get on top of how to push certain flavour profiles.

So I suppose to turn the question around, what are you hoping for from the brett?