It would certainly be impossible with SLS there has to be an exit for the unfused powder but I have printed internal passage way down to 2mm diameter but they have always been open ended though with blind bends and intersections in them (they are pressurisation airways so slight distortion of the shape is acceptable ) I was using 0.4mm jet and 0.2 mm layer height using nylon.
So worth a try using a 0.2mm nozzle.