I wasn't sure if this was a good idea but so far it's working out much better for me than the takeaway tek, which I normally use.
Baby lophophoras in a dub tub:
It's hard to see in the pictures, since they're wee little ones just a few days old, but the germination rate is good.
Soil mix is equal parts pumice and vermiculite with something like half a part of worm castings. Moisten, put seeds on top, seal it up. There are 6 small holes in the top tub with medical tape over them to keep flies away.