Adding banded tension to your shoulder work is guaranteed to trigger new hypertrophy gains. Just grab a couple of resistance bands and wedge them under the bench for overhead dumbbell presses.
The key is to lift the dumbbells all the way up to the top and hold them there for a couple of seconds in the contracted position of each rep.
So you spend maybe 5 or 6 hours a week in the gym. How much of that time is spent snapping towels or playing the soap dish game in the locker room? If you plan just a little and cut out the wasted time, you might actually build a decent physique.