Use the default datasession. But do not try to open the table via the datasession. Instead enclose the command in a TRY-ENDTRY inside a custom procedure:

PROCEDURE CheckForExclusive
LOCAL lcTable, llExclOK
lcTable = <path> + <tablename>   && This is whatever path and table
TRY
  USE (lcTable) IN 0 ALIAS excltest EXCLUSIVE
  llExclOK = .T.
  SELECT excltest                && Not sure if you want to close here or 
  USE                            &&   at end of program
CATCH TO loException
  llExclOK = .F.
ENDTRY
RETURN llExclOK
ENDPROC

You can call this as appropriate for your application. You can also do this with a small file. Open it with FOPEN() and this will work. You can set the FOPEN handle to a global attribute:

PROCEDURE CheckForExclusive
LOCAL lcFile
IF !PEMSTATUS(_VFP,"ExclusiveUse",5)
  ADDPROPERTY(_VFP,"ExclusiveUse",0)
ENDIF
lcFile = <path> + <Filename>   && This is whatever path and file
TRY
  _VFP.ExclusiveUse = FOPEN(lcFile,0)
CATCH TO loException
  _VFP.ExclusiveUse = -1
ENDTRY
ENDPROC

Then before the program closes, or whenever you don't want to have exclusive use, perform the following:

PROCEDURE ReleaseExclusive
  =FCLOSE(_VFP.ExclusiveUse)
  _VFP.ExclusiveUse = 0
ENDPROC

You can always check the status of exclusive access via the _VFP.ExclusiveUse being set to positive value.