I'm not 100% positive but I think i've seen somewhere that you steam them not sure if it has the same efficacy but it might be something worth looking into, also JCPenny's is currently having a sale on an 8 QRT pressure cooker for only $29.99
You only need a pressure cooker if you are dealing with any kind of grains. With BRF cakes you can get away with out having one. But it is best if you do have a pressure cooker.
i'm using wild bird seed and i don't have a pressure cooker, so, i just boiled them for about 2 and a half hours and i have no problems. the mycelium is growing beautifully.