What does "stuff it in the back right corner" mean?
As far as I know, it isn't a standard aviation term, it's just a casual phrase that he's using to emphasize or remind himself about the stick movement he needs. It's like your instructor telling you to "get dancing" on the rudder pedals: it's not an aviation term as such, but it's a very clear, descriptive reminder.

In a three-point landing you pull the stick all the way back after touchdown to keep the tail down. That helps to prevent unwanted pitch movements and gets weight on the tailwheel to help with directional control on the ground (as airspeed decreases and the rudder loses authority). Deflecting the stick to the right would be because of a crosswind from the right. Put those two things together, and the required stick movement is back and to the right, which is one "corner" of the range of motion it has.