If the user is holding down "Alt" on their keyboard when they start dragging a component, or a component group, duplicate the component(s) and start dragging the duplicate.

Note: Need to ensure proper threshold of dragging has happened before actually duplicating, so that the code doesn't duplicate in the exact same position without the user realizing, and then they have stacked components which they can't actually see. Basically, as long as the cloned components always start somewhat offset from the original, this should reduce the problem of accidental stacking.

Suggested by Cameron in a comment on Select Multiple Components