I found interesting trick for accessing normals from textures.
http://code.google.com/p/nvidia-texture-tools/wiki/NormalMapCompression Shortly, it allows to use DXT1 and DXT5 bump textures with same shaders. It’s important for editor because bump texture in DXT5 will be ready only at the last stage - game packaging. There will be small difference in object appearance during in-Editor testing because DXT1 is not good for normals, but I think it’s acceptable.