Hi rodsstuf,
Yes, you can start the case number at any specific number.
However, to do this, you will need to customize the stock Case screens & table. Currently, the case # is based off the Case table's RecordID. Therefore, to start a case at a specific number, you will need to add a new field in the table to store case #, i.e. CaseNumber. Afterwards, you will need to add a new case record in the table that will have the desired case number. Next, you will have to add some logic/calculations where any new cases will take the last recorded case # and add one to it.
If you need more assistance implementing this, I can put you in touch with a paid in-house consultant or you could look into our Method Solution Providers.