[arch-general] Setting global environment variable

I'm regularly connecting and disconnecting to a VPN using vpnc. The network I connect to has a transparent proxy which I want to set $http_proxy to. I thought I could do something like export http_proxy="proxy.whatever.com" in the /etc/rc.d/vpnc file, in the start and stop functions as necessary but exporting only makes the variable available to the child processes. Not to mention, I need this variable set for normal users also. Basically, I want to set and unset the variable when I connect and disconnect the VPN. Any ideas?