Yes!
Just copy http://getalby.com/.well-known/lnurlp/username to http://customdomain.com/.well-known/lnurlp/username
But your server has the incorrect mime type. Recommended as json but your one has octet stream (loaded as bin file). Some clients (web: astral or snort) will not be load your for. And you need to have a special allow strict header for cors request too.