I'm sorry... only read the first sentence of your post. I thought you could set it threw the IP phone itself but I don't readily see the option anywhere. I know you can set it through the use of the TFTP file, SYSTEM.PRV, and I believe through the use of the Nortel-i2004-B DHCP string.
If you are looking to secure the menu options you also need to enable the menu lock options with the Nortel-i2004-B DHCP string or within the SYSTEM.PRV file itself.
There's probably a better description of the whole process in one of the Nortel/Avaya technical configuration guides.
Good Luck!