It's not free, but I believe there's a way to use the google apps for business email service in this way.. I'm not entirely sure how it works though, since I always have the option to set the MX records to the Google ones.. Unless my lack of coffee is de-railing my ability to read what you're trying to say, because I re-read it.. Are you able to point your MX servers elsewhere, and just want to keep your domain pointers the same place? If so, that ~exactly~ how I set up my domains with the google apps services...