Thanks a lot for the good advice, epubgen made perfectly readable russian EPUBs out of a couple of FB2s. Somehow I expected this to be a lot harder, with a tool like epubgen, one could say that Nook supports FB2 fully. One small caveat is that the fonts take some space and what would normally be 0.4M book turns out as 1.5MB one. Well, given the fact that 16G microSD costs under $50 this is not a big problem
