How to add 'example.com' in the path of the action attribute?

I still could not solve my problem with using Drupal with a SSL proxy - see http://drupal.org/node/59996.

Now I'm looking for a way to add 'example.com' to the URL when I submit a page, so that

https://ssl.webpack.de/example.com/node/101/edit

is used instead of

https://ssl.webpack.de/node/101/edit

Any ideas?