Currently there is no way to do this with PM. I however found a great work-around: use the export function. Take, e.g., PM Classic. With the export you can specify quality, size, etc. of the images exported.
There are a few disadvantages to this solution of course, but with a little bit of scripting yourself you can circumvent these. The two major problems are:
1. Thumbs and html-files are generated as well, resulting in a lot of clutter and extra overhead.
You can get around this by editing and amending the ruby script and create your own.
2. Image files are called xxxx.yyy.jpg (where xxxx.yyy is the original file name)
A little command-line scripting gets around this.
Hope this helps,