Initially I used the following with no success;
export http_proxy=http://username@password:host:port
Worth noting I don't get a connection error directly, instead;
[root@pal ~]# sudo pear info PHP_CodeSniffer-1.2.1
No information found for `PHP_CodeSniffer-1.2.1'
Instead of using the system's http_proxy, set the proxy directly in pear's config;
pear config-set http_proxy http://username:password@yourproxy:80