You can use the centre stand to break the bead even when the rear wheel has been removed. Stick a flat rock or piece of wood that's about 50mm (2 in) thick under one leg of the centre stand. Now lift the bike horizontal, then past horizontal by 50mm so you can shove the 100mm thick tyre underneath, then lower the stand onto the bead.

If you don't use the rock/stone you are in danger of toppling the bike when you push it to one side to clear the rim.