Hi Matt,
I also have a '78 CB550, and I've found that balancing the motorcycle on the center stand with one or both wheels removed is not a problem. Of more concern is the possibility of accidently bumping it and tipping it over while in that state, but if you're careful and there are no dogs or small kids running around, its usually okay.
To remove the rear wheel only, I just put the motorcycle on the center stand. To remove the front wheel, I place a 1x4 block under the center stand, and then use a small bottle jack under the front edge of the engine to lift the motorcycle until the rear tire just touches the floor, which provides enough height for the front wheel/tire to be able to clear the front fender for removal. To remove both wheels, remove the rear wheel first, then raise the front with a bottle jack to remove the front wheel, no 1x4 needed since the rear wheel/tire is already out of the way. No doubt a scissor jack would be the way to go, but its not a must.