I would be tempted to remove the moss from the mesh, then, during a water change, superglue small patches separated by say 5mm over the area I want to cover. That should encourage the patches to grow together.
Theoretically, you might be able to take long strands of flame moss, glue them to the rocks horizontally, and then cut them into several sections with a razor blade. They could then start growing from both ends of each section, yielding multiple vertical strands.
Again, that's only theory. Maybe some of our moss experts can confirm.
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