Turn a single PF-style cake into a whole lot of mycelium spawn by blending it with corncob mush.
This will enable you to experiment with things like straw a whole lot more....
Your answer is corncob... This is sold as animal bedding. Again, check supermarkets, farm stores, department stores and pet stores. All of them have it.
Here is what you do...
Cover with water and boil it for about 30 minutes. A big pot, maybe 5 lbs or more of corncob is fine.
drain the water out (I know it looks dry and like it didn't absorb enough water... don't worry)
Place it in a covered plastic container to cool (use Saran or foil to cover if you want).
Take 1.. yes you only need 1.. PF cake and place in a clean blender (no I didn't say it had to be sterile).
Add 4 cups of water.
Blend for 2 seconds...
Start over.. I forgot to tell you to put the lid on the blender.
Pour this grey magical smelling slurry into the corncob.
Mix very thoroughly (yes I know how much water is in there.. read #10).
Drain excess water.
Cover with aluminum foil.
Place in warm (85f) location.
Wait 24 hrs (yes that actually is a little growth you see there).
Wait 10 days and it is completely colonized.
There is no need for sterile precautions if you already have a PF jar grown out. This gives you a huge amount of spawn to play with.. like for inoculating straw, or wood, or cardboard, or whatever...
A good rule of thumb for the amount of corncob is to use a standard dishtub (12"x14") and fill with the boiled corncob to about 4 inches. This is fine for 1 PF cake and 4 cups of water. This method works because corncob is extremely resistant to contamination (but not impervious) and because you are going way way overboard with the amount of inoculant. But it does work. I call it Massive Mycelial Slurry (MMS) and the process Massive Mycelial Inoculation (MMI).