How to avoid seams when lightmapping?

Is it possible to generate lightmaps that don't have nasty artifacts wherever there is a seam in the lightmap uv's? See the blocks bellow.

The art has nice normal maps and smoothed normals.

I've tried playing around with all the settings in the lightmapping window as well as generating lightmap uv's.

I've managed to get it to lay out the uv's so that there are less seams, but there has to be seams somewhere, and wherever there is these harsh edges appear.

Why does the lightmapper insist on baking in these seams? I don't see how this is possible if it's respecting the models normals...