After tinkering around quite a bit, here's what I've done.
Fix the partition table using parted:
sudo parted /dev/sdg
(parted) mklabel msdos
(parted) mkpart primary 8225kB 270MB
(parted) mkfs 1 fat32
(parted) mkpart extended 280MB 80.0GB
(parted) mkpart logical 280MB 80.0GB
(parted) mkfs 5 fat32
Write the signature (but not the MBR) to the drive using DD:
sudo dd if=phatnoise-first-1mb.img of=/dev/sdg bs=512 count=2048 seek=1 skip=1
Then, after booting, here's what I've got in bootload.txt:
BOOT0-0: OK
BOOT0-1: OK
BOOT0-2: Successful
BOOT9-X: Successful
BOOTB-X: Successfu
Notice the missing l? Also, I think it's missing a line here if I remember correctly.
The symptoms from the car perspective are the deadly blinking green light coupled with "NO CD" being displayed by my deck. I've got a VW Golf, FWIW.
Scarier is the logfile,
posted on PasteBin for convenience. Notice at the end, it gets spontaneously clobbered with binary data? Going to wipe this log and take it out to the car for another try.