Calling Stored Proc using EF4 with only some of the parameters

Question

I'm currently working on a new system that uses already existing stored procedures that are used in another system. They contain lots of logic for validation etc. so I want to use them in my new system and call them from Entity Framework 4 using WCF RIA Services.

Is there a way to only supply a certain number of params as some of the SP's have optional parameters. I've tried to delete parameters within the Model Browser in Visual Studio but this isn't possible.

I want to avoid having syntax like the following within my RIA Service:

this.ObjectContext.CallStoredProc("1234", "forename", "surname", null, null, null, null, null);