Add generic listener for TraceSources without config file

I want to redirect registration from System.Net to NLog:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <system.diagnostics>
    <sources>
      <source name="System.Net" switchValue="All">
        <listeners>
          <add name="nlog" />
        </listeners>
      </source>
      <source name="System.Net.Sockets" switchValue="All">
        <listeners>
          <add name="nlog" />
        </listeners>
      </source>
    </sources>
    <sharedListeners>
      <add name="nlog" type="NLog.NLogTraceListener, NLog" />
    </sharedListeners>
  </system.diagnostics>
</configuration>

      

        
        
        
      

    

How can I get it to work with code without app.config / web.config files? I cannot use them in Unity3D.