How to use portable Vim and Python together?

Question

vim

There are portable Vim, Python and this directory structure with them on Windows:

C:.
├─── portable_programs
│   ├─── vim
│   │   ├─── vim82
│   │   │   └─── vim.exe
│   │   ├─── vimfiles
│   │   ├─── _vimrc
│   ├─── portable_python
│   │   ├─── App
│   │   │   ├─── Python
│   │   │   │   └─── python.exe

Task: Run a .py file directly from portable Vim with one button using portable Python.

"Попытка 1"
let $HOME=$VIM
map <F5>      :! "~\.\..\..\portable_python\App\Python\python.exe" %<CR>

"Попытка 2"
map <F5>      :! "$VIM\..\portable_python\App\Python\python.exe" %<CR>

"Попытка 3"
$PYTHON = "C:\\portable_programs\\portable_python\\App\\Python\\python.exe"
map <F5>      :e $PYTHON %<CR>

Given that the above methods do not work, but this one works:
map <F4> :e $VIM\_vimrc <CR>

I realized that the problem is in the incompatibility of Vim's variables and the terminal.

Are there other ways to do this without changing the concept of complete portability?