If this is for CGI scripts under Apache, and Taint isn't on, then you can set environment variables in your httpd.conf or .htaccess files, using the SetEnv directive. If your server setup allows it...

I don't even know which directive-type you'd have to allow, except that it definitely won't work if AllowOverride is set to "None". ("In this case, the server will not even attempt to read .htaccess files in the filesystem.")