You're current method of providing a DMG is ideal, I think, for OS X. M$ even uses the same method...I'd almost call it a standard in cases where the payload is standalone. The only suggestion I have is to not minimize the window. This allows the user to drag the app directly to their Applications folder. Examples below...

http://wander.org/pub/stellarium-current.png

http://wander.org/pub/stellarium-suggested.png

You guys are rockin'!
Chris