If the site has a fixed dedicated ip address, ie you can reach the site by typing in the ip address instead of the domain name, then you could just point each domain directly at the ip address (don't use aliasing or forwarding or redirecting or masking or anything like that). The site will respond for any domain that points at the ip address. Then in your custom control you could detect the host name/domain name part of the url and show content accordingly.
The only downside I see is that if you create more and more sites with almost identical content, it could have negative effects on SEO for the primary site, since all the sites will have content that matches the same search terms. However this issue also exists even if you make separate sites with the same content so using multiple sites would not really solve anything.
You would need a custom contact form, but you could clone the existing one and add your logic.
Hope it helps,