Ok, resolvi isso. As etapas a seguir fizeram o trabalho:
cd ~
## [ get debian-live iso... ]
## create folder for mounting the iso
mkdir debian
mount debian.iso debian/
## copy install (contains initrd(gtk/normal) and vmlinuz)
cp -r debian/install livework/binary/
## copy needed files for installation
cp -r debian/pool livework/binary/
cp -r debian/dists livework/binary/
## create iso
cd ~/livework
xorriso -as mkisofs -r -J -joliet-long -l -cache-inodes -isohybrid-mbr /usr/lib/syslinux/isohdpfx.bin -partition_offset 16 -A "Debian Live" -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -o my-debian.iso binary
Espero que isso possa ser útil para outra pessoa também;)