Since there is no wording included that mentions the option to pay the additional amount by cash/CC, I have been going on the assumption that this is not going to be an option. If you contact customer service and get a definitive answer, please post it here.

And your question also has reminded me of another issue. If the lowest priced ticket available is $401, but there are also higher fares offered on the flights you want, will you be allowed to buy up to a higher fare class for say $598, in order to improve your upgrade chances while still not going over the next point threshold? Or will I be able to specify M class on an international itinerary so I can use my worthless SWU's, instead of automatically being booked at the lowest and non-upgradeable coach fare?

BTW, my new Flexperks Visa Card arrived in the mail a couple of days ago. Included with it is a special introductory offer:

1. Activate the card via telephone and spend $500 before 10/31/09, receive 15,000 bonus points.
2. Register for the second bonus at flexperks.com/freeflight15 and spend $2500 before 10/31/09 to receive an additional 2,500 bonus points.

Between the bonus points and the points for the spend, it adds up to 20,000 points = a free ticket up to $400 in value. The usual language to allow 6-8 weeks for bonus points to be added to you account is also included. Seems like a pretty generous welcome offer for basicly doing nothing more than you were already doing.

Full details are available at www.flexperks.com/freeflight15tc