Lemon juice might mask the bitterness by boosting one of the other basic flavors - sour.

(by basic flavors I mean sour/sweet/salty/bitter, oh & I guess umame. I have no idea in the world how to deal with the umame factor in Green Dragon).

But a piece of twisted lemon peel - no juice, no acid - considerably tames the bitterness of espresso, which is what led me to wonder about lemon extract & tincture.

I'll try to remember to pick up a bottle of lemon extract & give it a whirl.