All postinstalls should be able to run at do_rootfs time.
Patch on the mailing list.
http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=ccc394e7c6d3405b87fe862e50485f548b735da3
Verified on master branch. Commit ID:9ffee9add2d0380f4025e7a678a166f25a7d659e