Can't you use a wildcard? I think you can. Just announce *.youdomain.com -> your.IP. Then, you can just use a custom rewrite rule to transform subdomain.domain.

Can't you use a wildcard? I think you can. Just announce *.youdomain.com -> your.IP. Then, you can just use a custom rewrite rule to transform subdomain.domain.tld into www.domain.tld/sub/subdomain or something similar. From there, you're home free to do everything in your preferred language and framework.