There's no A/R option in batch mode. But you can fiddle with this...
Place each file on a separate SEQUENCE.
Export sequence 1 in stretch mode. This is an extra set-up step to overcome what may be a bug. The exported result can be deleted.
Go to Menu | FILE | EXPORT ALL SEQUENCES. Choose sequence mode and OK each prompt.
The quick result should be that all sequences (your individual files) have STRETCH applied.
A slower alternative...
Place each file on a separate sequence.
Apply the STRETCH effect to sequence 1.
Switch to sequence 2, right-click and APPLY LAST USED EFFECT.
Do the same for the remaining sequences.
Export ALL. Leave the A/R choice at Letterbox, not Sequence mode.