Auto-increment Custom Properties for SOAPUI testSuite

I am looking to auto-increment a Custom Property as my SOAPUI test is running. Currently my tests require that there be a unique portion, referred to as UniqueUserPortion, that get incremented as I test for uniqueness in usernames/emails. Is there a way for me to increment this custom property (#Project#UniqueUserPortion), as I will need it to be unique for the next step which is the check for unique username? Check for unique email:

    {  
  "UpdateIdentityRequest":{  
    "guid":"${#Project#UserGUID}",
    "emailAddress": "tomTestUser11@testit.com",
    "screenName": "UpdateUser${#Project#UniqueUserPortion}",
    "inputSystem":"${#Project#UserInputSystem}"
  }
}

Check for unique username:

    {  
  "UpdateIdentityRequest":{  
    "guid":"${#Project#UserGUID}",
    "emailAddress": "UpdateUser${#Project#UniqueUserPortion}@test.com",
    "screenName": "testUser2011",
    "inputSystem":"${#Project#UserInputSystem}"
  }
}