The last card to be dropped on top, is the spectator's secret card.
Secret card is shown in blue above for demonstration purposes.
Your thumb and fourth finger should be able to gently grip small pockets of the cards due to the way that you are holding the deck in the mechanics position.
Don't worry about your spectator seeing the pinky break as they should be viewing the trick from an angle that they can only view the sides of the pack that look completely normal.
With the secret card now on top of the deck, you are all set to perform the rest of your chosen magic trick.