With Precise, I used to create a USB stick using the so-called "Alternate" installer DVD with my own preseed.txt, update isolinux/txt.cfg with a new menu item that would pass my preseed file on the command line, and watch as the installer happily did all the right things to create a Ubuntu install on the hard drive of the machine I booted. With Trusty, the 'alternate' image has disappeared. Is it still possible to preseed a Trusty install, and if so, how do I get the d-i/ubiquity system to use my preseed file?