setting dev.acpi_ibm.0.events at boot time

[Dan Langille]

I'm trying to set dev.acpi_ibm.0.events to 1.  I'm failing.  I can set 
it from the command line:

$ sudo sysctl dev.acpi_ibm.0.events=1
Password:
dev.acpi_ibm.0.events: 0 -> 1

$ sysctl dev.acpi_ibm.0.events
dev.acpi_ibm.0.events: 1


This allows the special keys (screen brightness etc) to work on my 
ThinkPad X61s (see 
http://lists.freebsd.org/pipermail/freebsd-mobile/2008-March/010567.html).

I have tried /etc/sysctl.conf:

$ grep ibm /etc/sysctl.conf
dev.acpi_ibm.0.events=1

and /boot/loader.conf:

$ grep ibm /boot/loader.conf
acpi_ibm_load="YES"
dev.acpi_ibm.0.events="1"

Neither of which result in the desired results.

Clues?