webmail subdomain redirect

Hi,

We just setup a new RoundCube install outside cPanel and would like to redirect all (newly created) account there when we type webmail.newlycreatedaccountdomain.ext

like :
webmail.newlycreatedaccountdomain.ext redirect to : webmail.ourmaindomain.ext
webmail.anothernewlycreatedaccountdomain.ext redirect to : webmail.ourmaindomain.ext
etc...

Is there a way to achieve that automatically ?

Even more points if it works for already created accounts!

Thanks!