Have you tried simply stringing a ridgeline btwn the top ends of your stand with a tarp over it? That may not give you enough coverage if it's raining and windy given how close the ends of your hammock are to the stand. On the other hand, the low cost of some cordage and a WM tarp would surely make it worth trying.
Another option would be to put a ridge pole on top of the ends so it extends past the ends and drape a tarp over that.
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