如何在.NET中为自定义配置节启用configSource属性？

<?xml version="1.0" encoding="utf-8" ?><configuration>
 <configSections>
   <section name="customConfig" type="System.Configuration.NameValueSectionHandler" />
  </configSections>

 <customConfig configSource="customConfig.config" />
</configuration>

<?xml version="1.0" encoding="utf-8" ?><customConfig>
  <add key="setting1" value="value1" />
  <add key="setting2" value="value2" />
</customConfig>

using System.Configuration;

// 读取自定义配置节
var customConfig = ConfigurationManager.GetSection("customConfig") as NameValueCollection;

// 获取配置设置
var setting1 = customConfig["setting1"];
var setting2 = customConfig["setting2"];