>    A) gzexe all the executables.
>    B) lift the code from one of the other BSDs to do the same thing in the
>       kernel
>    C) Run from a filesystem that came from a compressed RAM disk, just as
>       the install media do.

C is my favourite.

for flash routers flash disk looks like

/boot
/netbsd.gz (contains kernel and cut-down system)
/config.tar.gz (contains configuration)

at startup (added after root fs mount) such commands are done
cd /
tar xzpf /flash/config.tar.gz


/flash is mounted read only, i just remount it in
/etc/save-config script that is run manually when needed.

8MB flash is enough