Heyas,
Sorry for the slow response here. You actually posted it during Origins -- one of the bigger summer cons. I just got back tonight.
It looks like McQuillan posted a pretty solid answer, however. Ultimately, a SINner should be able to cross the border without any real problems -- unless they're bringing something illegal.
Then it's just a matter of how well they can negotiate the issue. For purposes of quick resolution, I'd just do Etiquette + Charisma with a threshold equal to the TR.