I've seen a few apps get around this by packaging them in a standard .dmg and giving the user clear instructions ("just right-click") as the background image of

I've seen a few apps get around this by packaging them in a standard .dmg and giving the user clear instructions ("just right-click") as the background image of the opened container, or as the name of the app, or on the download website, etc. Although generally these have been fairly tech-oriented apps where the users would be likely to know the shortcut anyway!