Has anyone tried using one of the “Post Moderne” suspension seat posts? www.postmoderne.com/products.htm
The design would seem to overcome some of the issues of resistance to rotational forces as the “piston” part of the post is hexagonal rather than round. One problem though is that the smallest size seems to be 26.8mm, bigger than most unicycle seat tubes. But if you’re making your own uni and can choose your own tube size then this is another option to look at.