You are using an out of date browser. It may not display this or other websites correctly. You should upgrade or use an alternative browser.
alternatehistory.com
Anyway you could have Atheism/Agnosticism as an ethnic religion or ethnoreligious group. Something similar to what Catholicism is to Poles or Croats or like Orthodox is to Greeks or Russians.
Something like true X are Atheists/Agnosticism or all atheists/agnostics in this region are regards as members of same ethnicity distant from members of religion etc...