I got these onto the plugs with superglue. They were growing in the glass in my old tank, on top of some coraline algae. So when I scraped them they had a “base” of coraline I glued to the plugs, and they have been growing out for about 5 months.
but normally I do as Stan mentioned- small container filled with rubble in a low flow area and they will attach themselves to the rubble.