Tinkering around with a first-generation IO Dock and an iPad 3, I hit gold: There is an easy hack allowing you to build three additional USB ports into the dock.

• If you want to try, please have a look at the “Lessons learned” post first. It summarizes what I’ve learnt from others’ comments.
• This is the post with a walkthrough for the hack. Have a look at the how-to Youtube video as well.
• Could you hack the IO Dock II as well? It’s a redesigned device, so there is no guarantee, but it is easy to try out for yourself.