Apache :: How To Use Virtual Host IP Address In Request To Remote Address

My customer has an external facing Apache server that is acting as a reverse proxy to two internal applications. They have:

- external addresses for each app which resolve to different ip addresses, so app1.their_domain.com and app2.their_domain.com resolve to 77.3.170.10 and 77.3.170.11 respectively.
- the Apache server has two network interfaces with ip addresses 192.168.10.10 and 192.168.10.11
- the external ip addresses resolve to the above internal addresses
- the firewall between the Apache server and the internal app servers is configured to allow traffic from 192.168.10.10 to reach app_server1, and traffic from 192.168.10.11 to reach app_server2, both using port 7777.

I have configured a virtual host in httpd.conf for each ip, i.e.

Code:

<VirtualHost 192.168.10.10:80>
...
ProxyPass /app http://app_server1:7777/app
ProxyPassReverse /app http://app_server1:7777/app
RewriteRule ^/$ /app/app1 [R,L]
...
<VirtualHost>

and

Code:

<VirtualHost 192.168.10.11:80>
...
ProxyPass /app http://app_server2:7777/app
ProxyPassReverse /app http://app_server2:7777/app
RewriteRule ^/$ /app/app2 [R,L]
...
<VirtualHost>

This works fine in that the external address are being routed to the correct application, however the firewall is blocking requests to the second app as it appears the requests are coming from the Apache servers 'primary' ip address 192.168.10.10 instead of 192.168.10.11.

Is it possible to send requests using the ip address from the relevant VirtualHost?

Windows server 2008
Apache 2.2