Several ways come to mind.
Use a tiny but long rubber band, maybe cut a wider one to a thinner width, cutting the band so it's like a piece of string?
Another thought, to use super glue. Wear thin plastic gloves!!
One thing for sure, you will be amazed at how your normal hands change into all giant thumbed hands that shake uncontrollably!
Oh, with a brand new blade in your Exacto knife, shave just a bit of each seedling. Put the cuts together.
I saw the discussion on the Yahoo group. Welcome here, too!