In searching for /JRE_5_HOME|jre.5|jre5|jdk5|jdk.5/, I've only found TWO files which make use of the JDK5/JRE5 constants, so this might be fairly simple.
as/plugins/org.jboss.ide.eclipse.as.wtp.core/src/org/jboss/ide/eclipse/as/core/util/IJBossRuntimeResourceConstants.java
63: public static final String AOP_JDK5_DEPLOYER = "jboss-aop-jdk50.deployer"; //$NON-NLS-1$ 65: public static final String JBOSS_AOP_JDK5_JAR = "jboss-aop-jdk50.jar"; //$NON-NLS-1$ 93: public static final String JBOSS_ASPECT_LIBRARY_JDK5_0 = "jboss-aspect-library-jdk50.jar"; //$NON-NLS-1$
as/tests/org.jboss.tools.as.test.core/src/org/jboss/tools/as/test/core/TestConstants.java
45: public static final String JRE_5_HOME = System.getProperty("jbosstools.test.jre.5", "C:\\apps\\java\\jre5.0\\");