So, is the problem that you have accounts on both networks. You would be OK with just posting to both accounts, but for people who have the federation toggle on, they’ll get a duplicate view of your posts?

That actually does seem annoying. You probably can’t do anything about it, but it seems like it would be extremely easy to fix on the platforms’ sides. Since you are intentionally trying not to have people get dupes of your posts, they could just add the ability to tag a post with some identifier, then not show posts that have the same identifier, and rely on you tag your posts appropriately (and an obvious feature would be to automate that tagging and include it in the various “share to <other platform>” buttons).

If I’m interested in following you why would I subscribe to both your Threads and Mastodon account?