how to use MAKE_ENV or MAKE_ARGS to fix the right bash path?

[Anton Shterenlikht]

The porter's handbook has:

"If scripts are created with incorrect shebangs
during the build phase, the build process
(for example, the configure script, or the Makefiles)
must be patched or given the right path
(for example, with CONFIGURE_ENV, CONFIGURE_ARGS,
MAKE_ENV, or MAKE_ARGS) to generate the right shebangs."

This is indeed my case.
At least one generated Makefile has /bin/bash.
Before I start patching, I wanted to check
if I can sort this problem cheaply with either
MAKE_ENV or MAKE_ARGS.
What is the right syntax for use in the port's Makefile?

I cannot find any examples in the ports tree
of using either MAKE_ENV or MAKE_ARGS to fix the bash path.

Thanks

Anton