Did you realize that java.util.logging package uses the same (old-fashioned) style as log4j?
Using the wrapper class will mean you lose some of the features of log4j. log4j can include location information in the output; the documentation (see
PatternLayout) warns about the performance impacts of including that information so you probably would not use it on a regular basis, but it might be helpful to track down a problem. With your setup the location information would point to your wrapper class.
Using the wrapper class only to pass in the class does sound better than your other idea to get the class name out of the stack trace.