I'm not sure why anyone would need such a thing for a tablet, but just fooling around I discovered that the MyGica A681 ATSC Mini USB Stick is compatible with the TF700. For convenience I just plugged it into my Connect Dock, but I'm fairly sure it'll work with the keyboard dock or the OTG-USB adapter as well. The trick is finding the correct software to run it; so far the only app I've found that recognizes the A681 is PadTV-HD. The standard PadTV won't do it. I'm indebted to @tideee88 over on XDA for originally "discovering" this thing, on the Mad Catz MOJO. All I did was try it on my 700, and it worked.

Update: @tideee88 has just announced that the latest update to PadTV-HD no longer recognizes the MyGica. It's a free app, so if anyone needs the older version please PM me.