I've never done it as I usually kill my broms before they have a chance to propagate. Also - should I mount it like the parent or would potting soil be better?

Thanks!

I think it's big enough, and you can either mount it or place it in soil. Either way it will be fine.

They really don't get much of their nutrients or water through the roots, they are just for anchoring the plant. So where you put it or if you mount it doesn't really matter.

Just be sure the little one gets rain or watering to keep it going. Mine are all outdoors in or under my oak trees, but I still do make sure they're getting enough water, and I spray them with my orchid fert once in a while, too.