Domain Mapping: admin backend redirects

Is it all possible to redirect all backend administration to the non-domain mapped original URL?

E.G., I have my MU install at ....

I create a site for someone, and it initially is at:

We then map that site to

I would like users wanting to edit their content to be redirected to .... not

My reason: SSL certificates. I can buy one * SSL cert, versus an individual one for each new site.

Donncha's plugin claims to do this, but that plugin also breaks the wordpress functions dealing with checking if a user is logged in, so it messes a lot of other stuff I do