SQL 2008 R2 UDF with OpenQuery that uses parameters

Environment:
      MS SQL 2008 R2 Std.
      Linked Server to AS400 Db2

I have a Stored Procedure that does what I need and would like the equivalent User Defined Function.
My objective is to return a single value from a table within the Linked Server using a “WHERE” clause containing two criteria based on variables passed into the call.
I’ve been all over the WEB looking for a solution and believe that there is none based on the constraints inherent with User Defined Functions BUT……..
I thought I’d ask here none the less !
Thanks in advance..!
Here’s the Stored Procedure syntax that I would like an equivalent User Defined Function for :

USE [MyDb]
GO

/****** Object:  StoredProcedure [dbo].[sp_GetPartRev]    Script Date: 08/28/2014 12:34:24 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

-- =============================================
-- Author:            <Author,,Name>
-- Create date: <Create Date, ,>
-- Description:      <Description, ,>
-- =============================================
CREATE PROCEDURE [dbo].[sp_GetPartRev] @CoNo varchar(3)
                                      ,@ItemNumber varchar(15)
                                      ,@PartRev char(1) OUTPUT

AS
BEGIN

    declare @Command Nvarchar(MAX);
    declare @tick char(1);

    set @tick = '''';

    set @Command = N'SELECT @revOUT = IMPTRV FROM OpenQuery(IBMDA_SQL, '
                 + @tick
                 + 'SELECT PARTREV FROM LIB01.ITEMMSTR WHERE CoNo = '
                 + @CoNo
                 + ' AND ItemNumber = '
                 + @tick
                 + @tick
                 + @ItemNumber
                 + @tick
                 + @tick
                 + @tick
                 + ')';

    execute sp_executesql @Command, N'@revOUT char(1) OUTPUT', @revOUT = @PartRev OUTPUT;
END

GO