About boost_build (and boost-jam) it's very strange, I never separated bjam and its own environment settings. In Windows have a complex script to compile libraries and builder (bjam), it's not complicated to compile them, it's complicated to compile them in a temporary directory for 64 and 32 bit, and then copying each component (headers, libraries 32 and 64 bit, binary tools and their environments) in the right directories (for my needs).
The bjam tool is part of the whole distribution (<ROOT>/tools/build/v2), on ports it's dwnloaded from sourceforge, but the files are very different, it seems it's very old respect the one in boost distribution. It lacks clang compiler support (if I remember starting from 1.53.0 version). Anyhow, when I compile bjam in Windows (not the preferred boost platform), the executable (bjam) and all the environment files are copied into the directories bin and share under the root specified by the option --prefix.
Therefore, I see no patches to apply to all the boost-* ports, so I install all components without using ports, if it works I will try to modify the port Makefiles, but it whould be better if the this step is done by a port expert (I hope this sentence is understandable). Last thing, I never compiled it (on Windows) with ICU, MPI and zlib libraries, yes once, I don't remember what version it was, it was long time ago, but it should not be difficult to do it on FreeBSD, also I will try with both clang and gcc compiler. Good luck.
I'm open to any suggestions, criticism & Co.