MCC_PLAYBACK_ENGINE_VIDEO_ZOOM (28038) seems to work just fine for me.
Note that this setting is zoom relative to the window, and not relative to the video. So 100% will always fill the window. This is how zoom is handled under the hood - but not the same as the OSD shows you.
A value of 200% will act like the video window is twice as big, making the video half the size. And a value of 50% acts like the window is much smaller, making the video bigger. This is another reference to how one might be used to zoom, but it zooms the window, not the video.
While a video is playing, I just run this on the command line to test:
MC30 /MCC 28038,100