"Operation note permitted" when trying to change kern.sysv.shmmni on Mac OS X

I would like to change the shmmni parameter of my shared memory kernel settings, but when I try to write to it, I get "Operation not permitted".

sysctl -w kern.sysv.shmmni=2048

Output:

kern.sysv.shmmni: 64sysctl: kern.sysv.shmmni=2048: Operation not permitted

Can this be circumvented in any way? Why is the operation not permitted? shmmni should be a writable parameter... I can set the other shared memory params (shmmax, shmmin, shmall, shmseg)

I can change shmmni by updating /etc/sysctl.conf or by changing the setting via a launchdaemon, but these changes only have effect upon rebooting the system.

I would like to force-set it without rebooting.