git pull via PHP exec IIS

Easily the most difficult problem to diagnose that I have EVER experienced. I seem to be unable to call:

exec('call git pull', $output);

The process hangs and tends to take IIS with it.

exec('call git status', $output); //works fine

Here's what I've done:

• Generated RSA key added to github (passcode is blank)
• Everyone has permission on mysite/.git/, and Program Files/git/bin and cmd.exe
• Tried the ssl cert fix mentioned in other posts with 'slash' issue
• Tried using https:// instead of SSH
• Tried piping to stderr 2>NUL and 2>&1

Clearly, there's a permissions issue where exec calls cmd.exe which in turn calls git.exe, which in turn calls sh.exeto connect to github, which in turn makes use of git-pull and possibly git-send-packand GOD KNOWS what else.

I'm guessing 'sh.exe' determines the current user is IUSR and cannot find the RSA key to authenticate with.

If I could figure out how to ssh-keygen the IUSR account, I would have tried that.

If I could figure out how to exec git bash instead of git (via cmd.exe) I would have tried that.

Here's the question in it's simplest form:

How do I pull from my github repo via PHP's exec method?

The problem certainly seems to be with SSH, but I'm totally at the end of everything to try.

Help!