Unitarian, you just have to be searching.
If anything, the best I can see aiming for is some equivalent to cultural Judaism, where even non-believing Jews are invited to attend major ceremonies.
Hobby groups and community organizations offer a bit of this, but it seems like there's a fairly specific identity/culture gap that's not easily filled with anything else for non-Jewish atheists/agnostics.
But yeah the demographic of UU members is "High functioning non-contributors"