Using the JR Pass, can I reserve seats on the Shinkasen before arriving to Japan and physically receiving/activating my pass?

Hello everyone,

I’m traveling to Japan on December 2 and plan to activate my JR Pass on December 5. I’d like to reserve the first or last seats on the shinkansen to accommodate my luggage. Since seat reservations open 30 days in advance, I would like to reserve my seats on November 5, or as early as possible.

Assuming I purchased my JR Pass online through the official website. My question is: can I reserve shinkansen seats before arriving in Japan where I would be able to receive and activate my pass, or do I need to wait until I’m in Japan and have my pass in hand and activated?

Thanks in advance for your help!