Port maintenance: How to add extra source files to ports tree framework?

Hello,

I maintain in private a port (in fact, it is Espressif ESP-IDF for ESP chips).

The port itself is hosted via GITHUB. Download and installing of the sources has been
performed successfuly.

The port has several Python based scripts which start accessing the internet reeling in
several additions, but prior to that scripts check the system for meeting some compliance
criteria. For that reason the Python script downloads "runtime" a "contraints" file from
GitHUB, palces it usually into a local folder (usually ~/esp-idf/...) and checks Python
modules upon the content of that file, where several modules are listed with their required
versions. 
A general setup tool fails checking for Python's py-cryptography module, since the provided
FreeBSD port is advanced, while the requirement is behind. Commenting out that requirment
makes the Python script happy.

The main aim is to avoid permanent internet access when setup the IDF and preparing a package
for FreeBSD development hosts cut off the line. For that reason I'd like to do the following,
without preparing another extra port:

- additionally download the constraints file from another source
- placing the file in the propper staging/wrksrc folder
- editing that file according Python requirements
- placing the file in pkg-plist

Somehow I do not find a way to "extra" download from a different MASTERSITE and place the file
in the proper staging place before patching, then patch the file and so prepare the port and
the proper pkg-plist file.

Thanks in advance,

oh 


-- 
O. Hartmann