I know of only one JVM that has command line options to set processor affinity (to specify which processors to run on), but it is not generally available.
Setting processor affinity is an operating-system specific operation, and you did not say what operating system you are using.
On Windows, you can set it using Task Manager - right click on the java process, click Set Affinity, and uncheck the processors you do not want to use. Or you can get a copy of imagecfg.exe and add it to the java command line in run.bat.
On Linux, you can use the taskset utility to set the affinity of a running process or the current process. You can add it to the run.sh script - the shell will then run with those settings and jbossas will pick up the same settings.