ソリューションは必要ありません (情報共有のみ)
The SEP installer is calling /usr/libexec/java_home, which is a symlink to an Apple Java proprietary binary. Since all it does when invoked without arguments is return a value for $JAVA_HOME... I cheated and replaced it with a tiny script that just echoes out the literal string for the Java 7 Home directory. Et voila, I no longer need the soon-to-be-out-of-date Apple Java 6 to install SEP!
This doesn't excuse Symantec from fixing their installer so it does NOT require Apple Java 6.