With a lot more work, you can use a collection of wood, comparable to Manzanita branches, to form areas that could be planting areas for the emersed plants. You would need to work out how to keep the planting media in one place, so it doesn't all sift down to the tank substrate level. Doing it this way would let you include some marginal plants in the aquascape, but not set up a solid wall of plants that you can do with planter cups.
However you do it, you will have to spend some money. Why not spend it on good quality, easy to use planters?