+1  A: 

You should place the configuration in the web.config of you web app, making a section group that references back to your ProxyZipeeeService project. To do so, copy both the sectiongroup and the actual applicationSettings from your ProxyZipeeeService to your web application:

  <configSections>
     <sectionGroup name="applicationSettings" type="System.Configuration.ApplicationSettingsGroup, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
        <section name="ProxyZipeeeService.Properties.Settings" type="System.Configuration.ClientSettingsSection, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" requirePermission="false" />
     </sectionGroup>
  </configSections>
  <!--other stuff-->
  <applicationSettings>
     <ProxyZipeeeService.Properties.Settings>
        <!--your original appSettings-->
     </ProxyZipeeeService.Properties.Settings>
  </applicationSettings>

Then you can change the settings after your application has been deployed.

If all else fails, you could also make your ProxyZipeeeService library expose the URL as a public property, so it can be changed at runtime by the web application calling it.

I hope this was helpful.

Rewinder
Thanks so much - exactly the type of idea I was hoping for..However, I am getting a Parser error - "Unrecognized configuration section". I noticed you were able to insert XML nicely formatted in your answer. I had a terrible time doing that in StackOverflow and ended up using pastebin.com. How to paste my XML into this thread like you did?
John Galt
I fixed the parser error message...very subtle mistake. The great thing however is how you have helped me. Thank you so much for your assistance!
John Galt