The only idea that leaps to mind is that while the OUTPUT clause does not allow a subquery, it does allow a scalar function:

CREATE FUNCTION dbo.IsDistinctFrom

(

@value1 sql_variant,

@value2 sql_variant

)

RETURNS bit

WITH SCHEMABINDING

AS

BEGIN

RETURN

CASE WHEN NOT EXISTS

(

SELECT @value1

INTERSECT

SELECT @value2

)

THEN 1

ELSE 0

END;

END;

The OUTPUT clause would then become something like:

OUTPUT

Inserted.$identity AS id,

dbo.IsDistinctFrom(Inserted.col1, Deleted.col1) AS col1,

dbo.IsDistinctFrom(Inserted.col2, Deleted.col2) AS col2,

dbo.IsDistinctFrom(Inserted.isActive, Deleted.isActive) AS isActive

It's not perfect, but perhaps it gives you some ideas.