Okay, so it seems with Linux you can disable a CPU Core using:
echo 0 > /sys/devices/system/cpu/cpu1/online
According to /proc/cpustat and htop, only one core is active and being used by the Linux system.
The power consumption doesn't change though, so it seems the core isn't really disabled in the OMAP when doing this.
Seems like our current Power Management really is pretty simple, missing a few features.