Setting kern.smp.disabled causes it to work, too, of course...
sysctl kern.smp.disabled
sysctl kern.smp.disabled=0
sysctl kern.smp.disabled=1
echo 'sysctl kern.smp.disabled=1' >>/etc/sysctl.conf
DutchDaemon said:Probably/possibly, though it is not in the Kernel Tunables section of /boot/defaults/loader.conf (I assumed that was a finite list).