Job Cost Chart of Accounts - conditional account creation?

I could be misremembering (fantasizing?) about a way to have a model COA, that when used for a new Job Cost Business Unit, provisionally create the accounts, but the accounts do not exist in the F0901 until they get used. If the account was in the Model, then once it was used, either in budget or actuals, it would generate the AID in the F0901.
Can someone out there tell me how to set this up?

PattieK