[finestshops]

You can try a "low-tech" solution until you get a custom module from Carrie:
- add new shipping method called "Use my FedEx account"
- add $0 rate to this shipping method
- add new field to user profile called "FedEx account" so customer can enter it during registration, on checkout or in My account > Profile area and your order processing department can see it on backend. (if it's not saved in profile, they will need to call customer and get it before shipping).

would be more user friendly to show text field to enter FedEx account (if it's not saved in profile) right under "Use my FedEx account" method if it's selected and do a check if account number is actually entered before finishing checkout but this will require some customization.