From my discussions with Don at SkyGuard the route he is taking is to use the plug in puck for WASS gps source. I am skeptical that this will fly but who knows. The rough plan as I understand it is to create an acrylic or plastic enclosure that would allow the puck to be mounted on the top of the fuselage (weather protected). A certified antenna would be installed for out portion of the UAT. The unit would have to be permanently mounted and powered. Don said if/when he gets certification he will be selling a kit to of additional items needed to allow an Avionics Tech to provide a certified installation. This will probably require a field approval though as it would be very expensive to get an STC for every type aircraft that may use this option.
The unit has been through the first round of testing and the FAA requested some changes to the text being broadcast by the unit. SkyGuard has or is resubmitting this fall and the process starts over. The fact that the FAA is still working with them give me a measure of optimism.
There is a blog on the Skyguard site where he posts the status.
So far mine works pretty well, but would benefit greatly from permanent antennas for both the in and out. i thought about adding these at annual but may be chanigng aircraft in the near future and decided to not spend the money at this time.