There is a weather service listed in the AERAD. If memory serves correct it is @ RJFF, but I cannot remember for certain. I remember a VHF frequency being available in the general vicinity RJFK/RJFF. HF freqs are probably available as well.
The other way however is to make a landing runway assumption based on the METAR. If unnerved by doing this, use route 2 to put in the other arrival / approach option to have it ready as well.