Sign up for a new line of service (I suggest 1GB plan unless you're adding to an existing plan), apply the above promo code to your cart, once the promo is applied the phone price will drop to $280. Add a trade in/recycle phone to your cart to get the $200 gift card. It will check the ESN of the trade in phone to make sure it's not a 'bad ESN' phone, but it has no issues with phones that have never been active on your existing account and still have money owed on them on a device payment plan. (trading in my wife's 2013 moto X that still has a few payments left on it, i'll pay it off when i get the $200 gift card)
Once the phone arrives activate the phone, make a call, use some data, send a text. Package up your trade in phone and send it back to verizon to get your $200 gift card (within 2 weeks of verizon receiving the working trade in you'll get either a $200 bill credit or a gift card depending on if you are still a verizon customer or not) Go online and pay off the $280 balance on the new droid trubo so you can keep the phone. call verizon and cancel the new line. Your 'first month' prorated bill will have to be paid (if you picked the $50 plan it should be only a few dollars for the 1 day it was active).
I did a chat with a online rep and they confirmed all this will work, however the chat transcript i requested has not been emailed to me yet.