I think putting it in sideways would be not a bad idea at all, so the problem you 'd be left with would be how to prevent autorotation on devices where portrait and landscape settings are activated automatically in dependance of how the device is held.
Here emerges the question to MR experts I think:
1.) the portrait and landscape settings are RS sided so the RS knows the mode the book is being displayed in.
2.) AFAIR there is some CSS setting about that - could CSS this be used to prevent the auto-rotation of the map jpeg? i.e. declaring "this has always to be displayed in landcape mode" so that owners of sensor-controlled devices could turn them and look at the map w/o said map peing turned again too?