Sadly, it is not always possible to stay with the exact same make and model components for capt and stoker. As you probably already determined, the Thomson setback post would interfer with the current position of the stoker stem clamp on your capt seatpost.

Another option, same result... you could achieve a wider range of fore/aft positioning using a saddle with longer rails (ie: up to 85mm are available). The Fizik Aliante which appears to be the saddle on your RT2 probably has shorter rails (the usable flat section) than the Arione for example of another in the Fizik line.