I would use a temporary NameServer (say yy-project.com) and overwrite the /etc/hosts file in both your server and your developer machine. That way you can specify a second VirtualHost and start testing your application. When you get a second domain, you only have to replace it in your VirtualHost and remove the lines in your /etc/hosts files.
(edited)
The temporary vhost:
<VirtualHost *:80>
ServerName yy-project.com
ErrorLog /var/log/apache2/yy-project_error.log
TransferLog /var/log/apache2/ryy-project_access.log
LogLevel warn
DocumentRoot /var/www/html/yy.com
....
</VirtualHost>
Add this line in the /etc/hosts file in the server:
127.0.0.1 yy-project.com
And add this in the /etc/hosts file in your client machine:
IP_OF_THE_SERVER yy-project.com