Install archiso

pacman -S archiso

Create build tree in /var/tmp

cd /var/tmp; mkdir -p archiso-zfs/{work,isobuild}

Copy in proto ISO

cp -r /usr/share/archiso/configs/releng/. archiso-zfs

Edit archiso-zfs/packages.x86_64 and add:

linux-headers
libunwind
zfs-utils-staging-git
zfs-dkms-staging-git

Add custom repo to archiso-zfs/pacman.conf

[archzfs]
SigLevel = TrustAll Optional
Server = file:///$HOME/archzfs