While the man page for the Apple DHCP server implies that defining a DHCP option code with human readable form like your posted example is possible my own findings are that it only works with encoded data values. The encoded data values are in base64 format.
I have previously written a GUI utility to generate such values in a simple manner. I was hosting this on MobileMe but that of course has shutdown. However it looks like the following site http://dhcp-option-code-utility.mac.informer.com/ is providing a copy of my utility. Just use it to generate the right information and then paste it in to the /etc/bootpd.plist file.
I'm kinda new to working in Terminal. How do you open the /etc/bootpd.plist file for editing?
With Terminal.app open type the following
sudo vi /etc/bootpd.plist
The word sudo tells the computer to give you the access level needed to modify this system file. Of course the above is if you know how to use the old Unix command of vi.
Another option would be
sudo pico /etc/bootpd.plist
pico is a more modern editor favoured by some.