Please see here on how to access namebased vhosts:
http://www.faqforge.com/linux/contro...-a-dns-record/
Another alternative is that you configure the computers in your local network to use the dns server from ispconfig to resolve domain names and then create dns records in ispconfig for inofficial domains like "wordpress.tld" pointing to the internal IP address of the ispconfig server and then use these domains for the websites.