Step-by-step:

• Have your .obj file somewhere in your Runtime:Geometries: directories.
• Do a test import of your obj into Poser to make sure it imports with the correct scale and position without any of the import boxes checked.
• Make of copy of the ball prop's pp2. Open it up in a text editor.
• Find the file path references to the obj file. CR2 files generally have 2 references, I can't remember off hand if obj's have 1 or 2. Either way, change them so they represent the path to your .obj file. Save.
• Open up Poser and find your new prop in your Props library. It will have a shrugging Poser-dude Icon.
• Load it into your scene, apply material colors and such, then add it back to your props library.
• For distribution, you will need to include the .pp2, .rsr (thumbnail) and the .obj file. Also the image files for any textures.

Hope this helps.