Guys, Zone started out by saying he doesn't want a top box permanently mounted. Not suggestions for how to get one.
Anyway, the stock luggage rack is plenty to mount quite a bit of stuff. The roller bag up top plus the panniers mean you can already haul a lot of stuff. If you need more than that and are riding solo you can strap a metric ton of crap to the passenger seat itself and securing it to the sissy bar. There's really no need for any other solutions than the normal rack,
unless you insist on having a top box permanently on there, which I for one don't. I don't like the look, and much like OP prefer to strap stuff on when I need it only.