Hokuriku Arch pass and seat reservation

We are going to travel with our Hokuriku Arch pass during the Golden week. Therefor I would like to make reservatiion a.s.a.p. We have got our vouchers, but we are going to Japan at the end of April, so we don't have the real pass yet.
Can we make seat reservation anyway on a website like Eki-net? Or we will have to wait till we are in Japan.

Reservations can be made from one month in advance.

The JR East reservation site allows for online reservations regardless of where you bought the pass (but only those who purchased through the JR East website can pick up their reservations at ticket machines; others have to go to a ticket counter):
https://www.eki-net.com/en/jreast-train-reservation/Top/Index

Those who purchased their pass through the JR West website can alternatively use the JR West reservation website:
https://www.westjr.co.jp/global/en/ticket/overview/

The situation for this pass is particularly complicated because it is a product offered by two JR companies.