Yes, this would be a VERY good feature! Its very useful to be able to pause and have the software backup the recording a second or two.
The free transcription software called "F4" has this ability (they call it "spooling interval"), and also the ability to automatically insert time stamps and line numbers. The problem with that software is that it is a big file, runs in JAVA and does not run natively in Linux or in WINE.
Express Scribe is better and would be MUCH better if it included this simple feature that allows configuring the amount of backup.
I hope the developers read this and release a new version quickly!