Get ApplicationDataFolder-Direction in XML

I am using log4net to save logfiles via c#-application. The requiered app.config-data looks like this.

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section name="log4net" type="log4net.Config.Log4NetConfigurationSectionHandler, log4net" />
  </configSections>
  <log4net debug="false">
    <appender name="LogFileAppender" type="log4net.Appender.FileAppender,log4net" >
      <param name="File" type="log4net.Util.PatternString" value="C:\Users\Alex\AppData\Roaming\Log\logFile.txt" />
      <param name="AppendToFile" value="true" />
      <layout type="log4net.Layout.PatternLayout,log4net">
        <param name="ConversionPattern" value="%date [%thread] %-5level - %message%newline"/>
      </layout>
    </appender>
    <root>
      <priority value="ALL" />
      <appender-ref ref="LogFileAppender" />
    </root>
    <category name="testApp.LoggingExample">
      <priority value="ALL" />
    </category>
  </log4net>
</configuration>

The XML-File saves the logfile to the direction: C:\Users\Alex\AppData\Roaming\Log. If anybode use this c# application on a other pc (with a other username instead of alex) the logfile won't and can't be saved, because the direction won't exist.

If i ender "%appdata% in a microsoft-window i will get C:\Users\Alex\AppData\Roaming. It's the same function like

Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData)

Is it possible to change the value = "C:\Users\Alex\AppData\Roaming\Log\logFile.txt" more dynamically in the XML-Data, for example like:

<param name="File" type="log4net.Util.PatternString" value="${APP_DATA}\Log\logFile.txt" />

Unfortunately, it doesn't work. So do anybody know a other solution for my problem? I hope you can help me. Thank you a lot!