If you have a resort + ticket 'package', you can call and have it added to your package.
You can not preorder the photopass cd and then upgrade to pp+ at WDW while keeping the discount.
Options:
1. Skip pp+ and preorder pp cd ($120)
2. You can get the photopass cd order for $120 and add attractions+ at the park for $45 ($165 total). You would not get the meal photos with this option, just photopass pics and ride photos.
3. Order pp+ at the park ($200)
4. Add pp+ to a package, if you have one ($150 + tax)
Also, I really thought pp+ was worth it. I had ordered the pp cd when I heard prices were going up, so I got it for $100. Then pp+ came out and I got a refund for my cd and ordered pp+ for the original pre-purchase price of $170. So, I ended up paying $70 more to upgrade to pp+.