Cpanel offers multiple domain name add-on under one shared hosting account, the only problem is that it must be enabled by default by the server administrator and all add-on domains will be located in under your main account web folder.
For example you have a web site www.domain.com and you set-up the www.domain2.com as an add-on domain you get the following structure of the directories
Domain.com main folder:
www.domain.com/www/
Domain2.com main folder:
www.domain.com/www/domain2/
so as you see domain2.com will be placed under your main account, so everyone will be able to access domain2.com content as
www.domain.com/domain2/
You can set-up .htaccess redirect or mod rewrite redirect so that all users trying to access the folder using www.domain.com/domain2/ will be automatically forwarded to www.domain2.com