I can think of 2 ways of doing that:
1. if you're running NSM2008, you can do that with the new API support and a simple script.
Check this KB and the linked articles: http://kb.juniper.net/KB12730
In KB http://kb.juniper.net/kb12937 you can find sample scrips and the one named "address.pl" is an example of a script that create objects inside the NSM database
2. dirty way: create the objects in a FW device (via CLI you can script or edit the objects with notepad) and then import the device back into NSM...
For both situation you have to test it a bit.