Yes, I have used both/either Activated Charcoal or Bentonite Clay.
It's a fantastic suggestion and a seriously worthwhile addition. Why let there be ANY possibility of poisons reabsorbing if there's no need to let there be...and Activated Charcoal and/or Bentonite Clay will indeed, adsorb (possibly 100%) of everything released that's toxic.
HOWEVER, there's a strong possibility of either interfering with the action of the ES, so I've always taken mine about an hour after I take the olive oil/citrus...and then early/mid afternoon the day after. That works for me...but you might need to do a bit of self-experimenting to see what works best for you.