Nice - we're using a very similar approach now (procedure that runs just before creation) which I think will last us a good while. Glad to know it's worked out well for you :)
In our system, by default, all objects start at 1000. If a new account is created, and they want to increase a sequence to some value (say they already have 5000 invoices in QuickBooks and they want to start all new invoices at 10000 so they know every invoice #IN10000 and higher was created in our system), we have a simple interface that one of our support staff can go to arbitrarily increase the next value.