git push to a local directory with no .git in it

Background: I have to use plain FTP to upload content to my web site.  I keep a
local mirror of the entire site, then use an automated upload mechanism to do
the FTP step.

To release a git repository onto my site, I want to 'git push' from my working area to the release area in the local mirror. So what ends up as

    http://www.rpcurnow.force9.co.uk/git/mairix.git

lives in ~/homepage/git/mairix.git locally. That directory contains HEAD, refs, objects, hooks; I don't have a .git subdirectory in the middle.

If I cd to ~/gitwork/mairix (which is a regular working area) and do

    git push ~/homepage/git/mairix.git master:master

I get

fatal: /home/richard/homepage/git/mairix.git doesn't appear to be a git directory

presumably because there is no .git in it.

I could cd to ~/homepage/git/mairix.git and do things like

    GIT_DIR=. gitk --all

but what's the equivalent of this GIT_DIR trick when it's the remote end of a 'git push' that has the problem?

Cheers Richard