I may have missed something, but what exactly is the issue with the soil?
The nematodes may be a problem, but I'm on board with the baking thing. If you don't want to bake it, you could 'can' it (similar to most shroom teks). These plants seem to love the soil, and I think that sterilizing it could only help. When you kill all the organisms, you will gain them back as nutrients. Sure you may be losing beneficial bacteria, but who knows if your soil has any to begin with? Also, if you are having issues with growth, I would suggest using two separate containers, or just putting in a piece of plastic to divide the bin.
Now, everything I have said does not come from experience really. I have a good amount of experience with house plants, and vegetables, but not pot (yet). I have been reading and reading here on RIU for almost 3 years now, and as soon as I have a chance, I want to start my own small grow. That being said, feel free to disregard my advice, I just thought that I'd throw in my 2 cents.