I do not want to get in too deep here because they are not mods I use. But ...

The more recent versions of jqzoom ( the actual module rather than the zen cart module ) handle image swapping just fine. I have used it on a few sites with no problems. Somewhere there is a thread where I posted the code that I used but I have neither the time or the inclination to turn it into a formal 'module'. It is probably easier to use that feature to swap images than to hack two modules together.

But if you want to go the route of hacking two together then you need to understand that the zoom action is bound to the hover event when the document loads. If you swap the images then you need to re-bind the event. If that is all greek then ....

The only issue with IH is that the images need to exist before the zoom is triggered. They can't be created 'on the fly' at that stage. The solution is to pre-load the images at the bottom of the page which is not a bad idea anyway.