How about designing the adapter to connect to the external floppy port (ideally making it ultra-compact, accompanied with a nice case to make it matchy, matchy with the Amiga 500 case)? The only trouble that I can see is that the adapter would have to assume DF1: ownership this way, unless the Amiga is opened and the on-board floppy drive disconnected from the motherboard, or jumpered to be DF1: leaving DF0: available to the adapter. Just brainstorming ideas. :-)