You ask an interesting question. Thank you!
I looked at the Moodle code, and discovered that it is possible!
For my future reference, I will note here that we need to add the following two functions to "mod/hotpot/lib.php":
For examples of how these functions operate, have a look at how the following modules handle drag-and-drop:
I don't know when I will be able to do this, but if you can find some funding, that will speed up the process.