Replace BB for radiant

I have someone who wants to remove there BB in 1 room and replace with radiant. Doesn't seem like a problem-except they would like it on it's own zone. It is a WM CG boiler with 1 circ. and 3 zone valves. The room is about a 5,000 BTU/Hr load. If I tap in where it is at, it will only work when the old zone is calling. If I make it a new zone, how should I pipe it??? Any ideas-thanks.