You really don't have many choices here. If you have some in-vitro primordia mushrooms on your cakes, (I'm guessing they're still in the jars...) pick them off and throw them out. Do what you need to do in order to get a good casing system up (i.e. a layer of verm/soil on the bottom, then crumble or slice your mycelium over the verm/soil layer, then put a good layer of moist soil on top), by the time you get back, you should have a VERY thick layer of mycelium on top of the soil, ready to pin. Check out all the details on the Shroom Wizard's guide. Hopefully, the layer of mycelium wont be too dry when you get back. 
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My mind is corrosive...