I think you need to make a wrapper around your logger. Log4j maybe let you to programatically  enable/disable logging, but by creating a wrapper you can handle your future requiremnets(that now you can't see them) better and easily.
I refer you to the chapter 17 of The J2EE Architect's Handbook written by Derek C. Ashmore for writing a wrapper around your logger. You can find the PDF version of this book from the www.theserverside.com .