Exclude specific sub-domains from server where have wildcard server name

Hi, is it possible to have 3 server blocks with following server name? server block 1

server_name example.com www.example.com;

server block 2

server_name demo.example.com;

server block 3

server_name *.example.com;

reason i want to have like this, my main site will have server block 1, a demo will have server block 2, server block 3 will maintain the configuration for all other sub-domains that my client will create from my application.