I have just tested this - and got it to work. I need to amend the code in appapplication.getfilepath above to read this:

IF !ISNULL(this.cfirmdatalocation) AND 	m.cFile == 'BCS'  
	m.cFile = ALLTRIM(This.cfirmdatalocation) + 'bcs.dbc'
ENDIF 

now a call from the command file such as:

loCDE = CREATEOBJECT( 'cmDataEnvironmentCustom' )
loCDE.addcursor( 'Firm', 'curFirm' )
loCDE.openall

-- I have an debug stop right above the above code where i set the item below and resume.  

this.cfirmdatalocation = 'i:\bcstest\'