We recommend a separate support for each wheel, mounted outside the paper wheels. If you mount them inside the wheels, you will have less room for honing long knives and your setup will be limited to the small and medium blades.
But you need a separate support for each wheel not only because of the more room.
Even in better quality grinders/buffers the shaft is not parallel to the ground, and is higher on one side.
The paper wheels are also hardly ever of the same diameter, even new and even from the same maker.
Because of that, to hone at the same angle, you need to set the support differently for each side, i.e. for the left and right paper wheel.