install.cfg disklabel customization question

[Curtis Almond]

I would like to be able to do the following

1. Create a / partition of x size
2. Create a swap partition of x size
3. Create a /usr partition of x size
4. Create a ufs partition of the rest of the disk but it is not mounted at boot.

What I have thus far is:
# label disk 1
# IDE
ad0s2-1=ufs 3969000 /
ad0s2-2=swap 3969000 none
ad0s2-3=ufs 3969000 /usr
ad0s2-4=ufs 0 /usr100

Anyone know how to make /usr100 not mounted at boot time?

Or even better....
How can I create the ad0s2-4 (ad0s2f after boot) label but have
sysinstall not newfs it during netboot?

Any ideas would be great..

Curtis