One who reverse-pickpockets, that is, who puts something in people's pockets without their knowledge.
Rashid gave his sister a staunch, comforting hug and deftly slipped, like a reverse pickpocket, several bills of money into the un-protesting pocket of her gown.2004, Abraham B. Yehoshua, Hillel Halkin, The Liberated Bride, page 216:
reverse-pickpocket
verb
Etymology From reverse + pickpocket.
1
To slip something into someone's pocket or pocketbook, without their knowledge, sometimes as a gesture of generosity.
But when no one's watching he will slip hundreds inside palms and pocketbooks of poor people—reverse-pickpocket them—or bolt out of a car to help someone old hobble across the street.2001, Gary Smith, Beyond the Game, page 78: