On desktop, if you are using linux, you can configure system's proxy to route connections to port 9050 and add a nice rule to only do it for *.onion

On mobile, I remember talking with Victor about kmp-tor, but I wasn't sure how it behaves with WS (I'll test it for Robosats soon BTW 😬) did you check it out nostr:npub1gcxzte5zlkncx26j68ez60fzkvtkm9e0vrwdcvsjakxf9mu9qewqlfnj5z ?

Interesting topic setting different exit nodes on demand. Maybe you can do that with https://torproject.gitlab.io/torspec/control-spec/#redirectstream , and I know the new version for kmp-tor has planned to implement it