It really depends on how much you need to space it out. Without knowing the size of your bottom bracket shell I would just recommend spacing out as much length as you need all on the right-hand side (the drive side)
If you are using a much smaller shell than the motor was built for and intend to try and space it out equally on both sides then you need to get a little more creative. We do have a video here where one of our friends ended up simply tightening it down extremely tight with something that gave him extra leverage over the lockring, so clearly it is possible to get it so tight that it won't move the motor even if the black triangular bracket is not biting into the bottom bracket shell.
However there are other alternative methods as well, for example we do sell extras of those black triangular brackets that have the teeth on them.
You can buy multiple of them and use them as a spacer on the left-hand side and they will stack and bite into each other and the bottom bracket shell. If doing this you can cut off the mounting points on the sides of these brackets if you want to make it look nice when they stack.
You also have options like this stabilizer bar to help reduce twisting.
(the full suspension version BSBF-1 will only work with some sizes)
Another approach would be to to put it after the black triangular bracket if spacing it out on the left.
Another good idea would be to use red Loctite between the spacers and where they contact the bottom bracket shell, to increase friction and reduce the possibility of the motor twisting when under load.
Modifying conduit lockrings:
This method involves using Iberville 1" lockrings and slightly modifying to fit the axle.
What if you want to put all of the spacers on the right?
Putting all the spacers on the drive side definitely can work even with a 100mm motor on 73mm BB shell, although it might necessitate switching to an IGH on the rear, or using the low limit derailer screw on your derailer to keep it out of the lowest gear in addition to using the eclipse.
Custom Luna solution: Stay tuned but we will update this with more, here's an update