For all those who wondered, if there is a simple way to link multiple sites to one document root in an Apache config, here is an answer:
YES, it is possible.
ServerAdmin webmaster@localhost ServerName example.com ServerAlias subdomain1.example.com subdomain2.example.com DocumentRoot /var/www/website_source_code/
You can give multiple values to the ServerAlias parameter in you site configuration.
On an Ubuntu machine running an Apache web server, you can find your configurations under /etc/apache2/sites-available.