[support] 3 domains, 3 themes, 1 instance. Any clue?

Dear all, I have 3 separated domains: domain1.com , domain2.com and domain3.com. All three are on the same hosting. I want to share the same content, the same modules, but I need to have different views and blocks per domains. I was thinking the easiest way was to have 1 theme per domain. But how to do that? Another way? The domain access would be great but work only for subdomains, not 3 differents domains. Any clue? Thanks, Denis