using a proxy by default

my ISP uses a firewall to block all the ports except port 80 i hav to use a locally hosted server and the site must be accessible only inside the network. but i want to access an external SMTP server for php mail function. the intention being to send a confirmation mail to the registered users. i use a socks proxy in the mail client to get past the firewall how can i do it by php.. i use a proxy server to connect to the internet. i hav to use it to access any computer outside my network. plz dont suggest me to use CURLOPT_PROXY.. i don't want it to do every time. i want php to access the proxy every time it access a url. especially while using third party scripts i don't want to go through the entire code and make the changes just for proxy. if possible i also want to keep php from accessing the proxy server while accessing the sites inside the network