Using Brett

I think I have a botched batch of an American Strong Ale and instead of dumping it I am thinking of using Brett C. to salvage it.  I was just wondering how to go about using it.  Do I rely on the residual sugars (I have not taken a final gravity but it started at 17.5° P/ 10.72,)add dextrose to the secondary to up the sugar or just dump it in?  Any feedback would be awesome.

Ty