Если кому интересно, нашел решение.
Примерно вот такой запрос решает проблему:
|SELECT
| Жур.Date_Time_IDDoc as Позиция
|, COALESCE(uchastniki.Участники,'') as Участники
|FROM _1SJourn as Жур (nolock)
|LEFT JOIN (SELECT
| (CASE it2 WHEN '' THEN it1
| ELSE CASE it3 WHEN '' THEN it1 + ', ' + it2
| ELSE CASE it4 WHEN '' THEN it1 + ', ' + it2 + ', ' + it3
| ELSE CASE it5 WHEN '' THEN it1 + ', ' + it2 + ', ' + it3 + ', ' + it4
| ELSE CASE it6 WHEN '' THEN it1 + ', ' + it2 + ', ' + it3 + ', ' + it4 + ', ' + it5
| ELSE it1 + ', ' + it2 + ', ' + it3 + ', ' + it4 + ', ' + it5 + ', ' + it6
| END END END END END) as Участники,
| grID as IDDOC
| FROM (
| SELECT grID,
| MAX(CASE itNo WHEN 1 THEN rtrim(it) ELSE '' END) as it1,
| MAX(CASE itNo WHEN 2 THEN rtrim(it) ELSE '' END) as it2,
| MAX(CASE itNo WHEN 3 THEN rtrim(it) ELSE '' END) as it3,
| MAX(CASE itNo WHEN 4 THEN rtrim(it) ELSE '' END) as it4,
| MAX(CASE itNo WHEN 5 THEN rtrim(it) ELSE '' END) as it5,
| MAX(CASE itNo WHEN 6 THEN rtrim(it) ELSE '' END) as it6
| FROM (
| SELECT (
| select sum(1)
| FROM dt300 as ДокС2
| WHERE ДокС2.IDDOC = ДокС.IDDOC and ДокС2.sp308 <= ДокС.sp308
| ) as itNo,
| ДокС.IDDOC as grID,
| спрСотр.Descr as it
| FROM dt300 as ДокС
| LEFT JOIN sc89 as спрСотр ON спрСотр.ID = ДокС.sp308
| ) as OrderedItems
| GROUP BY grID
| ) AS AlmostAggregated
| ) as uchastniki ON uchastniki.IDDOC = Жур.IDDOC
|WHERE Жур.IDDocDef = 300