I recommend to build the entire system (with make) from sources, especially for the kernel which tends to be "unique", without modules. I will also provide the cross-compilers and the rootfs through a tar.gz. The installation is pretty easy: you create your partitions with 'fdisk', create the filesystem with 'mkfs.*', mount them and copy/extract the files to the fs partition.
I don't think I'll provide a special installer/script, that would require too much work for no real benefit.