Create new C::B project from make file project with existing code.
Build using C::B
Install via Plugins-> Manage Plugins -> Install New
On successful installation, File menu will have following item
Makefile Project With Existing Code
Select, browse to the directory to be added and select.
Tested on Ubuntu 16.04 with svn rev 13343 and wx30
Windows build should work with project file
MakefileProjectWithExistingCode_Windows_wx32_64.cbp