It only took a few minutes to put together a dozen soil blocks using a small, square plastic pot as the form. The trick is to get the soil mix (I used a basic potting soil with just a little perlite added) fairly moist and then pack it into the form very tightly until the moisture is oozing out. That way, the soil block will slide out of the form and still hold its shape.
I used a plastic deli container to hold the soil blocks; they fit pretty snugly, which should keep them from drying out too fast. The snapdragon seeds I was sowing are really tiny so they just needed to be sprinkled sparingly on top and then pressed down to make good contact with the soil. I'll move them to the mini-greenhouse tomorrow. Seedlings should start to appear in one to two weeks.