How to extend sustain in batch wav files?

I have a batch of sound samples which are too short (2.15 sec), and I want to extend the sustain to a total of about 10 seconds, meaning stretch the last 0.50 second of the file to 10 seconds. I can do this on each single file in audacity with paulstretch but was wondering if there's a way to do so in batch from the command line. Here is the original sample: original and here is the result I'd want: stretched