First off, I'm glad that IM uses the lqr library. Please feel free to contact me via mail for explanations, suggestions, discussion etc.
The manual supplied with the sources in the docs/ directory actually is comprehensive of all the functions in the library: the reference (Chapter 3) is incomplete, but the user's manual (Chapter 2) should explain it all (please, point to me any part which may be obscure and I'll try to clarify it).
For example, you can get the information about the seams which are to be carved from the "visibility maps", which are described in Chapter 2, in the section named "Dealing with the visibility maps (the seams)". Example 2.5 shows how to read out the seam rank ("visibility level") of a pixel.
For the purpose of smoothing, you could do it as follows (assuming a horizontal resizing): do the carving, read out the image and the visibility map, and parse each row of both in parallel. In the visibility map there will be regions with 0's only (which correnspond to the pixels which are kept) and others with strictly positive values (which are the pixels which were carved); this way you can identify which pixels in the output image belong to non-contiguous regions of the input image and smooth them.
In case of vertical resizing you would parse by column, of course. However, there's a problem when resizing in both directions at once. If you wish to introduce such a feature, you should be careful to implement it in two separate steps yourself. I may also implement it as an option for the library, but I am already working on other features, so it may take quite some time to see this in the release code.