In this case you have to trick the code.
CREATE PROCEDURE [dbo].[MyProcedure]
@pSelect nvarchar(max)
AS
BEGIN
SET NOCOUNT ON;
DECLARE @SQL nvarchar(max)
SET @SQL = 'select ' + @pSelect + ' from tabel1';
EXEC (@SQL)
--Remove the below line once you have added the stored procedure to the dbml file.
select * from table1
END
After creating the sp, drag and drop to the c# dbml file. then you can alter the sp by removing the line " select * from table1".
NOTE : if you dont have those columns in the table1, the direct values(any datatype) in the select statement like "select 1 as colmumn1, 'string' as colmumn2, cast('10/01/1900' as datetime) as colmumn3 from table1"