Michael,
Your premise is true, Sculpture only support One-To-One primary key association.
Which might be the common use of One-To-One association.
About "unique foreign key associations" is not supported in the current release, but we will add it in our task list to be delivered in the next release.
We do not study this case yet, so I can not recommend any instructions for you, but I think it will not be an easy task that you can provide with simple way.
Best Regards,