Yes, you'd just run all of the images through jpeg-recompress (from the GitHub repo linked above). They're already doing something like this to dither, so it's just a question of swapping out which command to run.
Incidentally, even where PNG is appropriate (images with crisp edges, such as text and icons) you can frequently get a large size savings by applying zopflipng, which uses an alternative GZIP compression algorithm to get a higher-efficiency compression, at the cost of greater CPU use for encoding.[1]
[1]: https://blog.codinghorror.com/zopfli-optimization-literally-...
