Can't use virtual targets, too many different combinations of options.
Ok, I changed my mind. How to create a codeblocks project that only uses makefile? Tried to File -> New -> Project -> Empty project, it said I must have at least one build target (Debug or Release).
Little feature request, I hope codeblocks would react in some way to opening an empty .cbp file. Like, allow viewing files in this directory, and save a correct project file on exit.