Unfortunately, Google's hybrid maps are not available as downloadable bitmaps, so, short of licensing NavTek's street data, this would be near impossible.

Even the topo maps would be pretty hard to integrate into Maemo Mapper now, as they are based on a completely different map identifier scheme (not X/Y; instead more quadtree-esque). Doable, but since I prefer the street data, I don't think I'll be tackling that problem at the moment.