User-account with no domain only subdomain

[Mercy]

I have an admin-account.

I want to use this mainly to provide people (not too many) with free accounts without allowing them to use a domain, only a subdomain to one of the domain i uses (alternative a path like this myfreehosting.com/user).

How do i set this up?

[ProWebUK]

setup the main domain as 'sub.domain.com' rather than as an actual subdomain the main account :)

Chris