Using 2 passes at different times.

Hi, Are you able to purchase 2 x 7 day JR Passes and use 1 of them the week before you travel to the snow at the beginning of your trip - travel to the snow and stay there for 2 weeks -then use the other one leaving your snow trip. If so would I get them both processed when I arrive in Tokyo and activate 1 of them at the airport with the stamp . and then get the 2nd one activated when departing Liyama station or would I have to travel to Nagano Station to activate the 2nd JR Pass with the first day stamp?
thank you Yvette