Well this is not strictly specific to Nokia tablets so this should go to forums.scummvm.org Check this
http://forums.scummvm.org/viewtopic.php?t=1837

For Nokia tablets there could be two specific scalers implemented - pixel doubling one for both N770 and N800 and arbitrary scaler for N800. N770 can only do pixel doubling in hardware, N800 can do any scaling ratio in hardware. The N800 arbitrary scaler could then do what you want. As for the port I am trying to maintain at http://fanoush.wz.cz/maemo/#scummvm there is no such work planned so far. First I prefer to finish keybindings for most engines for upcoming 0.10 version. Also I am not sure the output quality of such full screen scaler would be worth the effort, anything else than 2x scaler will probably look blurry/bad.