Comma Separated List as a derived field

in V9, we had some SQL Scalar-valued Functions like the below one. For example it takes CoNum and returns all the Salesmen in comma separated string.

CREATE Function [dbo].[xxx_GetSlsmanFn] (@CO CoNumType)
RETURNS nvarchar(max)
As
BEGIN
declare @tmp varchar(100)
SET @tmp = ''
Select @tmp = @tmp + A.slsman+ ' (' + coalesce(C.Name,'') + '), '
from CO A
left join slsman_mst B ON A.slsman=B.slsman
left join VendAddr C on B.ref_num = C.vend_num
where A.co_num = @CO

Return SUBSTRING(@tmp, 0, LEN(@tmp))

END

Previously in V9, dbo.xxx_GetSlsmanFn(CoNum) in a derived IDO property used to work, but not now.

How can I convert it into a Derived IDO Property? i.e. from a sub-collection, comma separated values of a property?