The best spot to do this is in the third chapter where you'll first encounter a Franken.
After you've lured one Franken away from the other, either punch (
) to stun him or wait for him to do his jump-attack, which will stun him after you've dodged his impact. Use your wrangler on him while he's stunned to rip some sort of antenna off his backpack.
Avoid the exploding creatures by walking away - you don't want to shoot them or else they will hurt you.
You will need to do this three more times to finally suck him up. Note that he will release a large amount of those exploding creatures after you've downed him. Just walk away a few steps until they explode and don't worry - he won't get up again.