Subdomain initially redirecting to a the multisite directory then staying there?

Hi!

I don't know if this specifically relates to Domain mapping - but I'm wondering if it's possible to have a subdomain set up for each subdirectory install where people can type in the subdomain address and then it redirects to the wordpress multisite subdirectory install straight away and stays there for the rest of the browser's time at the site?

I have my install setup as a subdirectory install for the sake of ssl etc (not having to purchase a wildcard ssl) but I think it would be cool if people could give their website address to people as a subdomain.