If there is neither a Linux partition nor an extended partition on the first disk, then there's only one place left, where a LILO boot sector could be stored: the master boot record.
In this configuration, LILO is responsible for booting all other operating systems too.
You should back up your old MBR before installing LILO and verify that LILO is able to boot your other operating system(s) before relying on this approach.
The line boot = /dev/hda2" in /etc/lilo.conf would have to be
changed to
boot = /dev/hda" in this example.