That's a great question!

By design the HD V-Twin has "more" stuff spinning in the North-South plane than a flat 6 - flywheel, crankshaft, plus the primary and clutch plates.
However, I think that most physicists will agree that stuff spinning in ANY plane will stabilize as much as long as it is equivalent mass at equivalent speed as long as that plane is not messed with too greatly.
At slow speeds, almost no angle of bank, dragging the rear brake (or as close to that as we can come with linked brakes) I would say that any RPM increase that you can maintain steadily will help.
Cheers,
Steve