log4net usa variables de entorno

Environment.SetEnvironmentVariable ("inicio_log", @ "d: / log");
Repositorio ILoggerRepository = LogManager.CreateRepository ("Repositorio");
XmlConfigurator.Configure (repositorio, configFileInfo);
ILog log = LogManager.GetLogger (repositorio.Name, "prueba");
log.Info (DateTime.Now);

<log4net>
  <appender name="RollingLogFileAppender" type="log4net.Appender.RollingFileAppender">
    <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />
    <file type="log4net.Util.PatternString" value="%env{log_home}/"/>
    <appendToFile value="true"/>
    <maxSizeRollBackups value="10"/>
    <maximumFileSize value="30MB"/>
    <rollingStyle value="Composite"/>
    <datePattern value='yyyyMMdd'/>
    <staticLogFileName value="false"/>
    <layout type="log4net.Layout.PatternLayout">
      <conversionPattern value="%date %-5level %logger - %message%newline"/>
    </layout>
  </appender>
  <root>
    <level value="DEBUG"/>
    <appender-ref ref="RollingLogFileAppender"/>
  </root>
</log4net>