You’re right, the miniaturised versions of Anubias are so congested and dense that it’s difficult to identify the rhizome. But you can simply attach the roots to wood or rock.
You can use ordinary Superglue to attach Anubias to bits of wood. I’ve never tried it with rock, but it might work.
I believe Superglue hardens to an inert substance, so it’s completely safe.
Just apply a dab of glue to a root, and stick to the wood. Don’t use too much glue because it goes white when submersed, which looks a bit pants.
Oh, and obviously when using Superglue, be careful not to get your fingers stuck. Or you’ll end up as a permanent part of your tank’s hardscape!