SHMMAX seems entirely broken in OS X 10.4.2

Has anyone been able to set kern.sysv.shmmax above 4MB at all in latest
OS X?  I just spent a while trying what seemed every possible
permutation of setting up /etc/sysctl.conf and editing /etc/rc directly,
and it just fails (symptom: sysctl shows shmmax as -1, and Postgres
cannot start).

Grrr.  Apple's been pretty lame about this from day one, but at least
it's been possible to do it one way or another.

(Curiously, it seems you can now change shmall after bootup in 10.4.2,
but that's not much help when you can't change shmmax.)
        regards, tom lane