Alternative for DIR() function in SQL statement

Question

Since Access 2010 I'm having trouble with the DIR() function in queries. The Sandbox mode disables this command -also the much used ENVIRON() function- by default.

For all clients I've changed the sandbox mode setting from 3 to 2. Recently a windows update or my system administrator set this setting back to 3 again for all clients.

I got a number of databases that use functions that will be disabled by this setting, and I'm getting a lot of complaints from 30+ clients.

In VBA there are other way's to check if a file exists, but in quey sql statements, I only know the DIR() function.

Example: (don't mind typing errors as I don't have the actual statement at hand)

SELECT.... [FIELD1] as IIF(DIR([FileName])="";null;"[FileName] " ) ... FROM...

"Is there another way to check file existence within a SQL command"?

OR

"is there a way -in VBA- I can set the registry setting for sandbox mode to 2"?

Note: Clients are running XP-32bit and win7-32bit and win7-64bit

Any help will be much appreciated!