The only safe way would be in a revolver using moon clips. Both of these rounds headspace on the case mouth. The 9MM shouldn't even chamber in a 380 and, unless held in place by the extractor, the 380 would drop into a 9MM chamber too far to be struck by the firing pin.

I've heard of revolvers capable of using 38 Super (9X23), 9MM (9X19), 9MM Makarov (9X18) and 380 Auto (9X17), all with moon clips and these should be entirely safe.