I have an idea that works in a different direction. I haven't read all 54 pages of this thread, so mebbe it's been suggested before.

I have an N810 with a Wayfinder license that expired some months ago. I can get it to work by setting the system time back; however, as someone here guessed, the software borks when it gets a time update via GPS.

Would it be possible to create an interface between the raw GPS data and the Wayfinder application? If that could be done -- or if the GPS software could be altered -- it might be possible to subtract a few years from the GPS timestamps as they are passed to Wayfinder
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Wayfinder seems to check system time versus GPS time, checking for large errors. For those not willing to set their system time back, you'd need a second interface between the system time and the Wayfinder app. I would guess that this would be much harder, given that datetime is a very low level type of function.

Just a thought. I think Sygic on my N900 stinks on ice, and I'd like to use my N810 as as dedicated GPS device.