consume external web service from asp.net page behind firewall

Hi, I hope this is the appropriate forum for my question. In my page, I call an assembly in the GAC from an asp.net page which consumes an external web service. It works great but not when I'm behind a firewall where I have to use a proxy. The proxy I have to use is "an automatic configuration script" in IE.
 I know you could use WebProxy.GetDefaultProxy() but that it's obsolete in .Net 2.0 and later. It works fine if I change the web.config file instead to something like this:
 
<system.net>
  <defaultProxy enabled="true" useDefaultCredentials="true" >
    <proxy autoDetect="True" scriptLocation="http://myproxyserver.mycompany.com/"/>
  </defaultProxy>
</system.net>
 
The problem is that I will deploy this solution to other companies and I can't really know what type of proxy server they use and I wou ...