I didn't load the top box when I did stuff like this; I put a couple heavy toolboxes on the ground on each side of the rear tire. Then I attached a ratchet strap to the handle of each toolbox. The other end of the straps attached to the support arms on my pannier racks (you could use the passenger grab rails too). Then I just cranked on the ratchet straps to pull the rear of the bike down towards the floor, and raised the front wheel. You don't have to stack a ton of weight on your rear rack, and the ratchet straps make it more controllable. Plus, since it keeps the counterweight down low, it makes the bike more stable when you're working on it.
I have two tool boxes that probably weigh anywhere from 30 to 40 pounds; that was plenty to get the bike securely winched down. If you don't have tool boxes like that, I bet a couple drywall buckets full of water would do the trick. I use the same method to remove the front tire on my Super Tenere; in fact, I used it recently when I removed the front forks and steering head.
"No matter where you go, there you are."