syphilis++, perhaps compiling the bar/baz sources to objects ends up too complex? E.g. more than 1 source files, complicated compilation flags, 3rdparty dependencies, lex+yacc preprocessing.
How about user either provides objects already compiled (and you have coded that in above post). This is the case where author distributes objects-only. Or *author* provides a tarball/src-dir containing all the necessary files and workflows (e.g. a Makefile which a) provides a target such as 'objects-for-inline-C' and b) reads optional ENV-vars for CC and other flags that Inline::C wishes to inject into this sub-compilation) to compile the required objects. This case is for when preparing for the public distribution of objects-only version. It can be run via a subshell, before Inline::C starts its own compilations.