Call NW Elite helpline in the US as they can upgrade you. I done it this way last year. (you can find the number upon doing a search in the NW forums)

The sectors that i couldn't get upgraded were done upon presenting my card at check-in.

Mind you though upgrades on continental are a little funny as they aren't really that well publicised in the FD manuals and on the internet site.

Can anyone confirm if PS's are still entitled to complimentary upgrades on Continental?