Sure, you can hop over to Settings and globally disable Bluetooth. But there has got to be a better/easier way to recover the on-screen keyboard without messing with Bluetooth, right? There is -- but it's only available right now if you're a developer (sign it using your credentials) or using a jailbroken system.
I've posted a little utility, which I call KeysPlease over on my website (direct application link) and on the ModMyI repository (thanks, Kyle!). I've added it to my iPad dock, and now when I'm in the wrong room I just tap the app icon to retrieve my soft keyboard. Bluetooth remains unaffected and I can keep working on whatever I've been working on.
The application works by dynamic linking to the Graphics Services function that attaches and detaches hardware keyboards. When run, it basically tells the system: "There's no hardware keyboard attached." Fear not. Your Bluetooth keyboard will continue to work and can toggle the onscreen keyboard, but the soft keyboard appears as well whenever you tap a text field. Of course, use this app at your own risk. Licensing details are here.