When a company pays for my ticket, and I spend extra on my own dime: I go into My Account - Manage Gift Registry - Send Gift Registry Announcements Send e-mails to family and friends to let them know about your gift registry. I then enter my email address. When I get the email, I gift myself however much I want. It can take several hours or even a day(?) for the funds to be available in your travel bank.
This way you can use money from your travel bank and from a credit card. Just note that you cannot do this and also pay using paypal.