In your .ssh/config write this :
Host git_heroku
Hostname heroku.com
User git
ProxyCommand corkscrew 10.3.100.211 8080 %h %p
Port 443
and in your .git/config change
[email protected]
to
git_heroku
The full line for a remote will look something like:
[remote "appname"]
url = git_heroku:appname.git
fetch = +refs/heads/*:refs/remotes/appname/*
git_heroku
is an alias; you need to change your git config to use that alias.