According to ericshliao you can boot from CF by putting "boot" in the config-file used for reflashing. I don't know if this also picks up a new kernel.
And there's kexec which is in some custom kernel (see this tread
) so you can test a 2.6 kernel.
I haven't tried any of them so I don't know exactly how it works.
ps. haven't read anything about a network boot...