Ubuntu Installation :: Install Using Network Boot From Local FTP

I want to perform a netboot install of Ubuntu using files sourced from a local network FTP server, and I cannot find the necessary installer files anywhere.

Reasons include:
* dead or flaky optical drive and no chance of replacing it
* optical drive is CD but iso is DVD
* several targets, so much faster to load repeatedly from local FTP than from an internet repo

What I can do with Fedora or CentOS is as follows:
1. On a second PC, download the relevant .iso and extract that to a directory (or mount it with -t iso9660 -o loop to make the contents visible without bothering to run the extract or using up more space). This makes all the files available but most particularly a ram fs and a mini linux installer, such as initrd.gz and vmlinuz

2. On that second PC, also set up the usual DHCP/PXELINUX/TFTP arrangements to cause the netbootable target PC to load those two files and run the installer. Also run FTP (or HTTP) on that PC

3. Netboot initrd.gz and vmlinuz (names vary) into the target PC. Answer the installer's questions, including choosing FTP (or HTTP) install method, giving the second PC's IP address, and an account and password, and path to the extracted iso. The rest is as usual.

I have not been able to do this with any Ubuntu netboot installer I have found so far. It either netboots, but then (seems pointless) wants a CD iso, or insists on pulling from a repo. Yes, I could create a local repo, but that seems to need a lot more work and space than setting up an iso on an ftp server. Is it simply the case that the Ubuntu family lacks this sort of netbootable installer or I have just been unlucky in searching for it.