Booking problem outside the Japan

hey,

I have a big question mark regarding the online rezervation outside the Japan!

I want to book all my train tickets before my Japan First time Trip but in last step it is written "you can not do it outside the Japan"

for example I want to book online "Nankai-Limited Express Rapit Beta" Kansai Airport to Tengachaya Satation.

Do you have any easy way ?