Different settings for different areas of a print.

I have a model that I’d like to print most of it at a low fill density, say 20%, but the top third I’d like to print at around 60%. Is there a way to do this or am I stuck with printing it in two pieces and cementing them together? I have Slic3r, Cura, and Simplify3d but do not see a way of accomplishing this. Thanks, Greg.

I’ve only read a little bit about this so far, but you might want to look at modifier meshes in slic3r:
Please let us know if you get it to work. I’d like to try this someday.

I tried it and it seems to work. Sometimes Slic3r crashes but that seems to be when I put in two models to print and then add a modifier mesh to one. If I add a model, set up its modifier mesh, then add another model, it seems to work OK.