The quick and easy way would be to boot to the install DVD, mount your root device then installpkg -root /mount/point path/to/package... For example...
mount /dev/sdx1 /mnt
installpkg -root /mnt path/to/pkgtools...txz
installpkg -root /mnt path/to/tar...txz
Alternatively you could probably extract the packages directly in your root directory, like this...
cp /path/to/package.txz .
zcat package.tgz |cpio -i
That wll not run the install scripts, but the commands will likely work fine for those packages.
Just to be sure, after you have pkgtools working, run installpkg or upgradepkg --reinstall on each of them to bring everything back into sync.