MPICH provides environment vars to make MPI compilers behave like spack.

var/spack/packages/mpich/package.py

@@ -38,6 +38,15 @@ class Mpich(Package):
     provides('mpi@:3', when='@3:')
     provides('mpi@:1', when='@1:')
 
+
+    def setup_dependent_environment(self, module, spec, dep_spec):
+        """For dependencies, make mpicc's use spack wrapper."""
+        os.environ['MPICH_CC']  = 'cc'
+        os.environ['MPICH_CXX'] = 'c++'
+        os.environ['MPICH_F77'] = 'f77'
+        os.environ['MPICH_F90'] = 'f90'
+
+
     def install(self, spec, prefix):
         config_args = ["--prefix=" + prefix,
                        "--enable-shared"]

var/spack/packages/scotch/package.py

@@ -10,6 +10,7 @@ class Scotch(Package):
     list_url = "http://gforge.inria.fr/frs/?group_id=248"
 
     version('6.0.3', '10b0cc0f184de2de99859eafaca83cfc')
+
     depends_on('mpi')