How to zoom with the Magic Mask tool?

I'd like to use the Magic Mask in the colour page to zoom in on the subject of a static image, without affecting the background. It's a common effect for adding a sense of depth to photos.

Could someone please suggest how to do this in the colour page?

I've got as far as masking out the subject, keyframing the zoom, and adding an alpha output - but that way I only see the subject and the background has been removed.

I imagine it's something to do with layer mixer nodes but haven't figured it out. Thanks for any tips.

You would need to use the clip twice. Once on V1 for the background, and once again on V2 for the cut-out subject (with alpha).