I was looking at the kindle 3 u-boot source code, and it contains these interesting bits:
include/configs/imx35_luigi.h: "uboot_net=tftpboot 0x84000000 u-boot.bin\0" \
include/configs/imx35_luigi.h: "diags_net=tftpboot 0x84000000 diagmon.uimage; run bootargs_diag; bootm 0x84000000\0" \
include/configs/imx35_luigi.h: "bootcmd_kernel_tftp=tftp 0x87f40400 uImage; bootm\0" \
So, it looks like instead of having fastboot or diags bootmode, it can instead boot images from a tftp server. I wonder now whether AdvancedToolKit has a built-in tftp server, or if you need to supply one in addition to the AdvancedTookKit program...