Not sure if these are helpful.
He ordered through a retailer, probably via mail flyer or something like that. Many of them use the Gift Cards as a part of their sign up.
To the OP, do you know what Dish is on your roof? The tech might just be able to use it, if it's a 1000.2 and if you buy the OTA, then yeah, he'd install it because you bought it - which you can do when the tech arrives. Calling Dish to add it probably won't work since you apparently ordered from a retailer but you can try that but if you buy it form the tech, he get's a commission. Something too think about