I did a bit more digging, and as far as I can tell it's not an option to change this setting. Details below:
At this point, I feel reasonably confident in saying that there's no option to change the modifier key for fine zoom using the mouse wheel. It's probably a hard-coded key setting. In theory you could modify the source code, but unless you really know what you're doing that's not a reasonable option.
Your remaining option is to make a feature request. Before making a feature request, it's always a good idea to search for similar feature requests, in case the developers have already considered and decided against implementing the feature you want. For example, see the discussion and reasons that the feature request "Usage of the mouse scroll wheel" was rejected.