Instead of making a new post into a Facebook group, simply share a existing status update/photo onto the group instead. If you make a direct post into the group, the Admins can tell right away it's spam and will delete it. If you share a status update into the group instead, the Admins can't tell right away it's spam and will be less likely to delete your post. The trick is to block all the admin. Although the Admins can still see you posted in the group, they won't be able to see the post you share. It will show as :"you don't have permission to see this post" it works because for the status update, permission is set to everyone. Everyone but the people you blocked. Share your results.