With the newest Java update (Java 2 Standard Edition 5.0 Release 4) Java 5 is finally the default VM on the Mac:
After installing J2SE 5.0 Release 4, J2SE 5.0 becomes preferred over Java 1.4.2, which will still be installed on your Mac. Applications run with J2SE 5.0 unless they specifically request Java 1.4.2
No need for hacks like this anymore.
