How to use DbContext.Database.SqlQuery(sql, params) with stored procedure? EF Code First CTP5

I have a stored procedure that has three parameters and I’ve been trying to use the following to return the results:

context.Database.SqlQuery<myEntityType>("mySpName", param1, param2, param3);

At first I tried using SqlParameter objects as the params but this didn’t work and threw a SqlException with the following message:

Procedure or function ‘mySpName’ expects parameter ‘@param1’, which was not supplied.

So my question is how you can use this method with a stored procedure that expects parameters?

Thanks.