I think i remember reading about this type of senario in a thread called Celestial Navigation?....Forget It! I don't have an answer for your problem, sorry,, but this is a case in point for that other thread.
Yeah...it belongs on the part of the thread where I said you need multiple GPS's. A Celestial Fix on lake champlain will put him somewhere in the adirondacks..since it is pretty darn hard to get a horizon there!! (G)