jumpseating
I have to agree... jumpseating while working for a foriegn company is not easy, and ID 90 may be the best way to go. Sure, many captains may not take the time to verify that CX is not on the agreement, may not know, may not care, may not want to be rude and say no, etc. and you may get on on a case basis.
Consider this: You know it isn't legal, and at best you are hoping ignorance will prevail, but now you have put the captain in the position of breaking the rules weather through nievete or just plain looking the other way. Either way, one or both of you should be uncomfortable with the situation... I wouldn't want to make a practice of this, but then again the everyone has their own view on what is right... I say dig deep for the $20, it's the cost of not living where you are based.
BTW CX is not officially on any jumpseat agreement in the US post 9-11.