Unfortunately, there is no such option in the original log4j class. But you can have a look at the class "org.apache.log4j.DailyRollingfileAppender". Method "activateOptions()" contains the following code:
scheduledFilename = fileName+sdf.format(new Date(file.lastModified()));
What you can do is extend the log4j class and change the behaviour of the method. Then you add your jar to JBoss and use your class in the log4j config.
Well... That's what I expected... Since it is HA production for time being I wil give it up.
Thank you anyway.