Bro do me a favor and ignore the deadlift request. i am 6'2" with very wide shoulders, my shoulder blades stuck out of my back plus i have some scholeosic that made it worse. i spent years trying to figure out the best way to builder muscle in the middle of my back between my blades. deadlifts are not the answer,they are great for the spine muscles in the lower back, but will not help, i repeat i dl over 500 and it did nothing for the muscle between the blades. you must make the 75-90 degree bb row your next bench exercise. what i mean is you must do between 75-90 degree pendley bb rows as hard and often as you would bench. these will thicken your muscle between your blades better than anything else. as assistant work do wide grip front pull downs and chin downs close grip. stick to 4x6 reps in general for the rows.
*Very important to try and stay as close to 90 degrees as possible. elbows out and up at least 45 dgree and make sure your rowing in the plain our your blades.. not below.. on heavy sets you can row lower but in general keep the form fairly good, i noticed a big difference when my rows got over 225 for a few sets of 8. i attack the row like i do the bench now, and it changed my back. trust me on this i tried everything possible. you need to go heavy and row, the best way to do that is the pendaly bb row. stick with the lift and you will see your middle back fill out. any questions pm me ill be happy to help.
I forgot to mention gain weight!! make sure you eat a good 1000cals over your norm a day, take weight gainer or what ever, but if you work the row twice a week and eat alot, you will put a lot of mass on your back..