As part of your jvm arguments you can set -Dlog4j.configuration=file:"<FILE_PATH>". Where FILE_PATH is the path of your log4j.properties file .
pleasePlease note that as of log4j2, the new system variable to use is log4j.configurationFile and you put in the actual path to the file (i.e., without the file: prefix) and it will automatically load the factory based on the extension of the configuration file:
-Dlog4j.configurationFile=/path/to/log4jconfig.{ext}