I am using snp.plotter to illustrate LD heatmaps along side a zoom plot. Here is an example of what I mean.

However, in this manuscript, they have images that look to be made by snp.plotter, but have gene diagrams overlaid, like can be done in LocusZoom. In the documentation for snp.plotter, however, I cannot find any option to add such a diagram.

Does anyone know how this is being accomplished? I know how to use Image Magick if an ad hoc addition is required, but at present I am not sure if the diagram is being added through the program or by another means...