how to make upstream acknowledge MPI port options?

[Anton Shterenlikht]

I'm the maintainer of lang/opencoarrays.
I offer users a choice of 3 MPI libraries.
It seems upstream cmake doesn't know of my options:

# make showconfig
===> The following configuration options are available for opencoarrays-1.9.3_1:
====> MPI (Message Passing Interface) support: you have to select exactly one of them
     MPICH=off: Parallel processing support via MPICH
     OPENMPI=on: Parallel processing support via Open MPI
     OPENMPI2=off: Parallel processing support via Open MPI v2
===> Use 'make config' to modify these settings
#

-- Found MPI_C: /usr/local/lib/libmpi.so (found version "3.1")
-- Found MPI_Fortran: /usr/local/lib/libmpifort.so (found version "3.1")

(which are for mpich)

Obviously upstream doesn't know or care about
FreeBSD ports options.
So how is this supposed to work?

How can I affect upstream build process based
on port options?

Thanks

Anton