Don't need to use another computer to remove the forever root. Install & run "Voodoo OTA" first since you need to be root to allow this to keep root. Use something like Root Explorer, go to /system/bin and look for mount_ext3.sh. On mine there was a backup copy of the original file so I just renamed backup_ext3.sh to backup_ext3.sh.old and renamed the mount_ext3.sh.bak (or whatever it had been named) to mount_ext3.sh. If you don't have a copy of the original mount_ext3.sh then remove the lines at the end of the file:
chmod 4755 /system/bin/sh
chmod 4755 /system/xbin/sh
chmod 755 /system/app/Superuser.apk
BUT be very careful not to change anything else in the file or the update could still fail.