JR-West All Area Pass online seats

We have bought the JR-WEST All Area Pass. The we land in Kansai, we are taking a train to Hiroshima. I don't want to book a seat for that day because I don't know how long it will take us to get through inmigration, if the plane will ariive on time, etc. But we can book it for the day that we go from Hiroshima to Kyoto.

Is it possible to do that online before getting to Japan and actually have the pass itself? If yes, how please? I have spent hours and I can't find anything.

Thanks.

Hello

Have you had any answer to your question? I will be there in July and cannot find any answer ....

Online seat reservations are possibly only if you purchased your pass through the JR West website. However, I found the the website to be difficult to find (no clear links provided), understand (confusing labels and explanations) and use (for example, if you enter any connections that don't have direct trains running between the two stations, e.g. Kanazawa and Osaka, you will get kicked out and have to go through the entire login process again).