I can get it to do this too (v1.0.8)
turn on "Hide wp-admin"
turn on "Hide Login Page"
"Access error type" to 404
set "Set custom page 404 url" to "https ://google.com"
go to https: //your domain.com/wp-admin/
wp_safe_redirect will only redirect to a local url, not external to your site
when...