Sure, this isn't too hard. Setup two appenders in your log4net config.
<appender name="RollingFile1" type="log4net.Appender.FileAppender">
<file value="log1.log" />
<appendToFile value="false" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%-5p %d{hh:mm:ss} %message%newline" />
</layout>
</appender>
<appender name="RollingFile2" type="log4net.Appender.FileAppender">
<file value="log2.log" />
<appendToFile value="false" />
<layout type="log4net.Layout.PatternLayout">
<conversionPattern value="%-5p %d{hh:mm:ss} %message%newline" />
</layout>
</appender>
Then just setup two loggers, one to each appender.
<logger name="MassTransit">
<level value="INFO" />
<appender-ref ref="RollingFile1" />
</logger>
<logger name="MyLogger">
<level value="INFO" />
<appender-ref ref="RollingFile2" />
</logger>
You just point each logger at the right file and call it a day. If you have questions about how any of these elements work, I'd hit up the manual: http://logging.apache.org/log4net/release/manual/configuration.html.