Pulling the scrotum out along the shaft and holding them together.
This forms a slot, or pouch between the two that, if gripped tight enough can be fucked.
This resembles and gets its name from a Kangaroo pouch
Man #2: Shrink Wrap?
Man #1: No, that doesn't do anything for me.
Man #2: Roo Pouch?
Man #1: Sure, me first!
Man pulls his balls out and holds them along his shaft while the other sticks his cock in the space and proceeds to fuck it.