Can I have an Identity Column based on the Primary Key instead of the table

I have a table where the primary key is the Claim Number.  If I have more than 1 Claimant for a Claim Number, I would like the identity column (Claimant Number) to increment by 1.  Therefore, for Claim Number 12345, I would have 2 records where the Claimant Number would equal 1 and 2 respectively.  However, now I have Claim Number 67890, and again I have more than 1 Claimant.  I don't want the Claimant Numbers to be 3 and 4.  I want them to be 1 and 2 again since this is a new Claim Number.  Can this be done using an Identity Column, and if not, does anyone know of an easy way to accomplish this? Thanks...