Add more quality and unique content to your site, start doing linkbuilding to your site to drive traffic to your site. After getting some decent traffic to your site, apply for adsense. There is a chance for approval.
Own domain is not the mandatory requirement.
The unique content with good stuff derive users to visit one's domain.
Always give a good look at the search keyword which are driving traffic to your site.
Improve them to attract more users. Same approach i followed with my blog too.
You can always write and ask what you did wrong in the first palce.
Then you must be sure that you don't break their rules ( having adult content, pharmacy related, etc ).
After that you should be approved.
example: if you have a news sport site you will be approved.