Replace rear brake disc with wheel still on?

[Fazerider]

I guess you’re trying to avoid the slightly awkward job of persuading the wheel back in without a spacer getting nudged out, but think you’ll just make task harder.
If you can find a thin plank of wood about 2ft long (a bit of old floorboard or timber cladding is ideal) you can place that under the back in line with the bike. Roll the wheel on until it’s in position, then as you raise the end of the plank it’s easy to get the spacers to stay with the wheel as  you squeeze it into the swingarm. Once it’s roughly in line with the axle holes you can chock the plank to that level and you’ve two hands free to wriggle the axle in.