Your explanation of price-bridging is confusing.
To OP -- Use your Orbitz ticket to enter a theme park. Then do your upgrade. Your Orbitz ticket was purchased at a discount. Let's say you saved $25 compared to buying from Disney. If you upgraded before using your ticket, its worth to Disney, in the upgrade process, wouldn't be the price you bought it for, because Disney doesn't have that info. Disney only knows the wholesale cost they sold the ticket to Orbitz, perhaps $50 less than buying from Disney. So your PH upgrade would be $64, but you would also owe the $50 to bring your ticket up to Disney's current price. Your upgrade would cost $64 + $50 = $114.
But if you entered a theme park first using your Orbitz ticket, then did your PH upgrade ($64), Disney would go ahead and upgrade the value of your ticket to Disney's current price. In other words, you would only owe $64 for the PH upgrade, and you would keep your discount.