The other option is to do the sim in the UK (or other JAA member state). Flight Safety is in the UK these days. (Farnborough).
The difference is one is employed by the Training provider, eg Flight Safety and is a TRE (Type Rating Examiner) the other is employed by the regulatory authority, in this case, the UK CAA. Those examiners are not cheap and can be quite hard to get hold of. I would hate to have to pay for them to go to the US.
Not knowing what Citation your friend is looking at does make it tricky.
If he cannot do the sim in the UK (or EU) and he doesn't want to pay for another session at Flight Safety Int then I *think* the only option left is to fly a piston twin...
( I am not overly familiar with this route)