After r20032, there's a good chance that Rockbox USB will work nicely on PP5022/PP5024 devices. Here are some builds for the affected devices with Roxkbox' USB stack enabled. If you notice any trouble with USB transfers, please post in this forum thread. If you see any other trouble not related to USB, switch to a standard build and see if it exists there, then file a bug.
And here's the source (which is the exact same as standard r20032, since the only thing changed is in the Makefile).