I ended up using a service from Yahoo, SmushIt: http://www.smushit.com/ysmush.it/. It can handle several hundred images at a time. I tried uploading 2,500 and it froze, but had no problem doing 400-500. The compression isn't quite as good as Google's, as Google Page Speed still says it can compress some of them an additional 3-8%, however, I've noticed that Google will sometimes reduce image quality, whereas SmushIt maintained exact quality 100% of the time.
