Came up with a simple solution that works for me. A 3.5mm stereo plug with wire I cut off a dead set of headphones - just plug that in, select onboard speaker and all is well.

Since it is just wire rather than a hard antenna, it is easy to loop it over the top and hold it in place with a small dab of blue tack. Comes off easy for stowage and nothing to really catch. I do live in a big city so it might not work quite so well out in the sticks :-). Been using that almost since I got the N800 with no problems (but all I listen to is generally just FM radio).