Someone a while back made an applescript to launch ebook-edit and accept drag-and-drop as well, but I forget when/where.
Something similar might work here.
Of course, this would be far easier if OSX worked more like linux, where OS Open With is defined via .desktop files specifying
a command to run.
Or Windows which uses actual executables for linking and associating stuff.
Or maybe just anything other than OSX, with its odd habit of using those weird app bundles with their inscrutable contents. I assume because it is "easier" for the technologically unsophisticated.
Apple does not make things easy...