Using webspace accociated domains as multi-domains. Is that posssible?

magiclyfit.com does not have a dedicated IP. But at my webhosting provider I have added other domain-names to magiclyfit.com webspace, which can be used similar to subdomains.
They work within the same webspace, I just have to tell them the virtual path.
So how can I use those other domain-names in the same matter as multi-domain-names?
Thanks for your help.