Since no one answered, I'll try.
I do not know for your transponder. But the data comes from the efis. So a direct efis to gps connection will work. The efis also sends altitude data to the transponder (assuming you are not in Canada and have a blind encoder). Some transponders, like the GTX327 I have, can re-send the data out, in which case that can go to the gps. It's daisy chained, so if the transponder is off, the data does not go thru to the gps. I do not know if your transponder has this serial data out capability.