There is no dedicated "Call for Alley-Oop" button in the Wii version of NBA 2K12 My Player. The Wii control scheme (Wiimote + Nunchuk) lacks the button granularity of PS3/360 versions.
Note: Wii version is a distinct build (Visual Concepts) with simplified physics and stripped features. Consider 2K13+ on PC/PS3/360 for full My Player control suite.