Let's address the more basic problem. There is almost (I DID say "almost") no case where you would want a true 1/1 table relationship, and it is for the reason you stated. If you have relational integrity enabled, you MUST populate both tables, and that turns out to be mechanically very tricky.
Typically, one of the tables is different from the other and is perhaps dependent on the other in some way that isn't reciprocal. IF that is the case here, the dependent table must be the MANY side of a 1/Many and if you REALLY wanted that key to still be unique, there is a way. You make the relationship say 1/Many but then separately put a uniqueness index on the foreign key field in the dependent table. Then if you don't have a record in the dependent table, no problem. But if you do then it simultaneously has to satisfy the relationship AND the index constraint.
Here is the techie viewpoint on 1/1 relationships: In theory, a record's PK uniquely identifies the record in and of itself. That is, no other field in the table contributes to the uniqueness of the record. (If it did, your PK isn't really Prime.) If you have a 1/1 relationship, that means that the PK in your table also uniquely identifies ANOTHER record in a different table. In such cases, you should collapse the two tables together because they both depend on the same key. The concept of "purity of purpose" thus suggests that the PK should be in the same table as EVERYTHING that it identifies. But a split 1/1 pair of tables violates that concept. Note that there ARE exceptions to this concept and not everyone looks at it in exactly this way.
