I've found sysinstall and its ilk to be extremely bad about being able to
do _anything_ out of the ordinary.

Setting up a separate swap area is pretty easy but you may find it a bit
touchy if you can't boot diskless. Allow me to explain.

If there is a server on the net that you can use to boot the VAX diskless
into NetBSD (a Linux or *BSD box works great for this) then create an
installation on that system (just untar the sets, make the devices, and
edited the rc.conf file.) Then boot diskless. Now partition your disks
either manually (which is what I typically do) or if you want interactively
with the disklabel program. Run newfs on all the partions you've defined,
then mount them up under some directory (the directory 'a' was used by lots
of folks) in the order that they will be mounted. This will probably
involve making the /var and /usr directories by hand to facilitate
mounting. Extract the sets into this mount point, make the devices, edit
rc.conf and then edit fstab to mount things in the right places. Voila'
you're ready to go.

--Chuck