If you flip it upside down, placing soil in the lid with the container resting on top, you can make a mini terrarium like setup for micro greens. Then you can drill wholes in the lid to allow for draining and place it on a saucer. (I have done this for a couple containers and it works)
boiling water is the only method I know of that doesn’t leave any contaminants, though I never found a need to bake them.
I just plop my substrate in a bucket with boiling water in it, then give it a quick stir before spreading it thinly on a mat allowing the hot water to evaporate off, leaving the substrate dry.