To do that, you'd have to make a subclass (basically, a new xmodule type) that has the dependency. I'm not sure I entirely understand the use-case for this change, though. A key question, I think, is: do you expect this to be a baseline that a professor edits and expands on (essentially, an example of how to do something), or is this more of a template (meaning, you just want to be able to plug in a few key values).

In the latter case, I think a subclass/new type of xmodule is the right way to go. In the former, I think it's better to keep it as a template, and add this dependency (which basically says, you can use modal images in any instance of an HTML block).