As I (mis)understand it, you may have a look at the ways suggested in these threads, increasing the Stroke Weight as desired after creating the centre path:
That you, I found a family easy work around. Using the line tool. first create an outline of the inner stroke, then connect the different paths using the line tool. At this point then merger the paths and now the inner and outer segments can be manipulated.
A family easy work around…
Thank you for sharing.