What do you think of doing drop sets for assistance/supplemental work as a way to get more volume in less time? Instead of 3-5 sets of 5-20 reps, it would be 1 set that includes a few drops.
For the upper body, try rest/pause training.Another way is to pyramid back down the 5/3/1 ladder reaping out the sets
For cycle 1 it would be5 x 65%5 x 75%5+ x 85%5+ x 75%5+ x 65%
Sure, he mentions drop sets in the beyond book under 2-2-2 hypertrophy, though I agree with above poster regarding rest-pause an an alternative.
I do it all the time if I'm running short on time. Say bicep curls, I'll do my 10 reps, then just move down the rack until I hit my 30. Or pull ups, I'll go pull ups, chin ups, fat guy pull ups, lat pull down until I hit 50.
Check out Jim's website. There's a new article about programming assistance work.