Yeah I think I know what you mean. Brown rice flour and vermiculite is the standard, should work pretty well.
Then you'll have a layer of verm at the bottom with the cakes on top? Should be fine. Don't overdo it with misting them.
Oh one step that I missed the first time I did that is that apparently you need to dunk your cakes in water for a few hours after they have colonised. So, you inoculate them, wait for them to colonise, and then remove them from the jars. You then soak the cakes in water for a few hours before carrying on. The reason this matters is that the mushrooms are mostly water. Each time you get a flush, the cake loses a lot of water and you need to replenish it between flushes. But, keeping them too wet all the time tends to raise the risk of contamination by bacteria.
Good luck! Its an exciting hobby. I don't know why, but I just love the sight of growing shrooms. I think I'd even consider growing non magic shrooms, its just awesome.