Add these PowerShell commands to the "Installation" phase of your assembly:
(New-Object Net.WebClient).DownloadFile('https://bitbucket.org/pypy/pypy/downloads/pypy3-2.4.0-win32.zip', "$env:appveyor_build_folder\pypy3-2.4.0-win32.zip") 7z x pypy3-2.4.0-win32.zip | Out-Null $env:path = "$env:appveyor_build_folder\pypy3-2.4.0-win32;$env:path"
Then you can call pypy.exe from anywhere in your assembly.
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