I was looking through my old emails, and I realized that I still haven't found a resolution to this. Andrus vaguely mentioned that there might be a good reason why you aren't allowed to, but I wasn't able to find that reason.
So, to recap, here's my scenario: I am normalizing the schema for a request ticket database. I wrote an importer using Cayenne, but I wasn't able to determine how to specify the PK for an object when that type is set to have the PK assigned by the database. The PK is not meaningful (in that its value has no inherent meaning), but it is used as the unique token to identify each REQUEST - after all, it is the PK - and I therefore must keep this value consistent from one schema to the next. I need to have the DB generate PKs for the production code when creating new requests to avoid PK collision, as we have two replicated MASTER servers, one for each country we are located in; the anti-collision strategy is to have PKs generated by the database where PK MOD 10 is a different value on each MASTER.
