The picture you show is the only factory-available two-sabot setup, and is a to shoot a .357 bullet in a .50 gun. In a .45 gun, you'll just shoot the .357 bullet in one sabot. There are no ML bullets available that I am aware of smaller than .357, and certainly no sabots for them. Centerfire rifle bullets will be too long to stabilize in your rifling anyways, you'd have to use pistol bullets which wouldn't fly flatter than available ML bullets even if they are lighter because they are less aerodynamic.
I am aware of at least one guy who machines his own .45 sabots from PVC that go from .45 to .308, and shoots centerfire .308 bullets. Of course, this is in a Savage smokeless ML with a custom fast-twist barrel.