How can I convert a *.img file to a basecamp *.gmap directory?

I have a number of single OSM .img files for various countries. I want to use that map information in Basecamp on Windows. How can I convert a single .img file to a .gmap directory that I can copy into a Basecamp directory to use it in Basecamp? By a .gmap directory, I mean a directory that contains .xml, .mdx, .typ files and a Product1 directory and a .mdr directory. Basecamp appears to recgonize such maps just by copying the *.gmap directory into C:\Program File (x86)\Garmin\Basecamp\Maps, without any registry entries required.

I have found solutions that allow me to access the maps data but not by using a *.gmap directory that gets loaded into the Basecamp Maps directory. I would rther not deal with requiring my computer to have the GPS plugged into it or even the SD card plaugged into it. And I would rather not use a solution which requires messing around with registry settings (and the administrative access that requires).

Thank you for any assistance anyone can provide.