I'm pretty sure you'll need physical access to the machine to fix it.
First, try booting to single user mode. That may fail trying to run
ksh though. On PC's you can pass boot parameters to the kernel through [lilo|grub] or through OpenFirmware on SPARC. If there's any type of equivalent on AIX try passing
init=/bin/sh as a boot argument.
That should get you at least a shell, but that's all. Your root fs may be mounted read-only, so remount it rw. You should then be able to fix the permissions. Afterward make sure you
sync. The kernel will probably panic if you try to exit or reboot, so just expect that. When you're done reset the machine.
Good luck, and may the Force be with you.