Best option is using ComplexHeatmap.

It's often easier to generate figure parts (e.g. heatmaps) independently and then assemble them manually into a final figure using another software such as Inkscape or Illustrator.

You cannot do that with heatmap.2() due to the way it lays out the graph. Try the aheatmap() function from the NMF package. You should be able to use thelayout() command with these heatmaps.