there is a workaround... to use the ecert and use a foreign CC (even with foreign billing addy)...

use the main united.com site as usual to apply the ecert... but then 'accidentally' use the wrong expiration date and/or billing address. this will cause an error after 2-3 attempts, after which your itinerary (with the ecert discount) will be put on hold and tells u to call web support.

call web support and give your foreign CC. they'll accept foreign CCs on web support.

the trick is to get the itinerary HELD in the system with the ecert first!