Originally Posted by Stripe
Don't sign in with your Worldperks number. AFter you select your flights, continue to the purchase process as a guest. There will be a place to enter your OnePass number.
This is basically the same way NW elites book flights on continental.com.
Actually it doesnt matter if he signs in with his WP #, NWA's reservation system can hold two FF #'s and will upgrade you according to the highest level, he just needs to be sure when booking that he enter's his OP # as the program he wishes to receive credit on