Pass variable to pkg-install

[A. Nooitgedagt]

Hello,

How can I pass a variable like "GROUP" from Makefile to pkg-install?
pkg_install needs to do things depending on a variable in Makefile. Is there
something like PINSTALL_SUB like PLIST_SUB?

SCRIPTS_ENV or " MAKE_ENV GROUP=${GROUP} " didn't work (in Makefile)
Neither did " GROUP?=${GROUP} " (in pkg_install; where "?=" doesn't seem to
be allowed.)

Sorry, I'm new to this list.

Aldert