SQL Server: Inline Queries Across Linked Servers

I’ve had to run a scheduled T-SQL query from one database to another linked server for an import operation. I'm finding that I have to do some comparisons between the result of two subqueries in order to get the proper value for one column. So the results I want would correspond to something like this:

Insert into localTable (columns)

Select col1, col2, col3,

CASE 
      WHEN subquery1result > subquery2result THEN subquery1result
      ELSE subquery2result

END As col4

From server.schema.dbo.table1

Where [stuff]

Note the reference to the linked server… First you have to set up the Linked Server in SQL Server, then you can reference the external database table as [LinkedServerName].[SchemaName].[DataBaseOwner].[TableName]

To flesh that out a little more, if I filled in those subqueries in-line:

Insert into localTable (columns)Select col1, col2, col3,

CASE 
    WHEN (select MAX(T2.datecol) from server.schema.dbo.table2 T2 where T2.id = T1.id) > 
         (select MAX(T3.datecol) from server.schema.dbo.table3 T3 where T3.id = T1.id) 
    THEN (select MAX(datecol) from server.schema.dbo.table2 T2 where T2.id = T1.id) 
    ELSE (select MAX(T3.datecol) from server.schema.dbo.table3 T3 where T3.id = T1.id) 

END As col4

From server.schema.dbo.table1 T1

Where [stuff]

But that doesn’t work – using subqueries in a CASE statement like that won’t fly.
I would normally do these subqueries as user-defined scalar functions, but I can't seem to make one that queries tables in a linked server. And I'm not allowed to modify the schema of the database on the linked server (vendor system).

Any ideas on another way of doing this? I suppose I should copy all relevant values into a holding table (on the local server) & then run the import from there instead of importing directly from the linked server. I was just hoping I could keep it as a straight 'Insert Into... Select From' query in a single step.

I think I stumbled upon a "good enough" solution (which suitably horrify a proper SQL-Ninja):

Insert into localTable (columns)

Select col1, col2, col3,
(Select MAX(DC) From 
   (
      select MAX(T2.datecol) as DC from server.schema.dbo.table2 T2 where T2.id = T1.id
      UNION
      select MAX(T3.datecol) as DC from server.schema.dbo.table3 T3 where T3.id = T1.id 
   ) as U
) As col4

From server.schema.dbo.table1 T1

Where [stuff]

It seems to work, though the query is a bit on the slow side (7 seconds to return ~2K rows). Well within reason for a nightly batch job though. Basically the UNION of multiple inline queries forms a set of it’s own, which we can further query from. In this case we’re choosing the Maximum value returned from two different queries.