Answer:

First off, being honest, drpop sets aren't that great for building muscle. They will make you FEEL like you're pushing your muscle harder, but in reality, you're using less and less weight, which generates less mechanical tension on the muscles, which is the key driver of muscle growth.

You're increasing fatigue but you're not really building muscle.

That being said, there are techniques you can use to increase the intensity when you are doing drop sets on selectorized machines.

• Use multiple pins - Set one at your heaviest weight, one at your next drop, one at your next drop, etc. Just pull the bottom one out when you are done that part of the drop. This decreases the turnover time between drops, increasing the intensity of the exercise as you don't have to take the time to put the pin back in.
  
  

• Pin-pulling spotter - An even better way is to get someone else to pull each pin for you so you can keep tension on the muscle the whole time. Just graze the plates at the bottom for the split second it takes to whip out the pin. You may even want to try not grazing but actually holding it slightly above the next plate and letting the plates drop from there (make sure it is only a fraction of an inch - don't break anything to do this).
  
  

• Leaning, pin-pulling spotter - An alternative is to have the spotter lean down on the weight stack while they pull or reset the pin so you can keep pushing against it (at the bottom of the movement - push just enough to maintain tension in the muscle, not enough to throw them off).
  
  
• Leapfrogging - If you only have two pins, try leapfrogging them (this only works with someone doing it for you). Your spotter will take the pin that they just pulled out and insert it higher up while you are still doing your set (preferably wait until the peak of the movement when the weight is stopped for a second or two and being very careful of fingers the entire time). This trick allows use of the multiple-pin technique without using all the pins in the gym.