Create a new vhost and add Listen directive.

[code]
# -----------------
Listen 8181

# You can also add client-site.com.clients.com to your hosts file.
# client-site.com.clients.com -> 192.168.1.134
# Make it run on 2 ports at the same time.
<VirtualHost *:80 *:8181>
DocumentRoot C:/projects/clients/client-site.com/htdocs
ServerName client-site.com.clients.com

<Directory C:/projects/clients/client-site.com/htdocs>
allow from all
Options Indexes FollowSymLinks Includes ExecCGI
AllowOverride All
</Directory>
</VirtualHost>
# -----------------
[/code]

Add firewall rule to allow connections to and from port 8181 for all private and public networks.

Add a port forward at the router level from port 8181 to your IP:8181

Restart or reload apache

I am assuming that you have created C:/projects/clients/client-site.com/htdocs

Bonus: if you're running WordPress as well you can change links pointing to the external IP address on the fly.
Do replace all occurrences of 1.2.3.4 with your real ip and add this snippet to wp-config just after the opening

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