This is a trivialised example highlighting my situation:
ProxyPass /google/ http://www.google.com/ ProxyPassReverse /google/ http://www.google.com/ <VirtualHost 127.0.0.1:82> ProxyPass /google/ http://www.yahoo.com/ ProxyPassReverse /google/ http://www.yahoo.com/ </VirtualHost>
In this case a request "http://127.0.0.1:82/google/" will try to go to http://www.google.com
I have also found that a ProxyPass defined in main will take precedence over actual directories available in a vhost - eg if in above instead of the VirtualHost having ProxyPass rules its DocumentRoot contained a directory named "google" the Proxy would still be in effect.
Per the apache docs, I had been led to believe any "main" definition would be overridden by a VirtualHost able to satisfy the request.