Transfer a block of agar nutrients with the mycelium, about 10mm on a side, because the nutrients will promote growth down into the wheat. When the soil layer is a solid mass of sclerotia, save the sclerotia and discard the wheat. Sterile procedures can be discontinued at this point. Put a large amount of sclerotia in the bottom of a tray. On top of it put a porous medium, which might include, shredded aspen, chopped corn cobs, tree bark, sand, peatmoss, etc.
Sphagnum peat is a little inhibitory due to acidity.
The other items are neutral. Conifer sawdust is good if it is heat dried to remove volatiles. Hardwood sawdust is ideal without processing. Then wash and water it often being sure to remove all water each time, so oxygen can diffuse in. Holes might have to be avoided in the bottom of the tray to keep the mycelium from growing out.