Short answer: GRUB.

Long answer:
In message <199608140117.SAA11764@baloo.ucsc.edu> you write: 
> Linux to NetBSD.  One of the "nice" features of the Linux installation was
> that the boot loader (LILO) would let users type: dos to boot dos and
> "unix" to boot Linux.

Ick, this involves modification of the partition table probably, which
is not pleasant.  Of course, it might use another spot on the disk than
the MBR, but then you have to keep track of it...

> All of the boot loaders that I'm aware of that load NetBSD, autoboot,
> bteasy, etc. use either a numerical digit or a function key to select which
> partition gets booted.

Try OS-BS.  A new version is due out "Real Soon Now" as of a few years ago :)
Still quite good though.  Probably also quite good in conjunction with GRUB.

> Is there anyone who has made LILO boot NetBSD, without the benefit of
> having any Linux partitions on the disk, or who has put the described
> functionality in another boot loader which we could use in our lab?

GRUB has way more functionality than LILO and if you're looking for
a single solution for multiple free OSes, GRUB is it.  See:
http://www.uruk.org/grub

> If not, does anyone have an idea how hard it would be to make LILO work with
> NetBSD as the primary support OS, i.e. as the place to store its
> configuration files.

Interpreting a (non-live) BSD FFS is not very hard, and well-documented.