DD-WRT - Host-based forwarding

Yes you can do this; you'll need the Pound add-on.

WHAT POUND IS:

1. a reverse-proxy: it passes requests from client browsers to one or more back-end servers.
2. a load balancer: it will distribute the requests from the client browsers among several back-end servers, while keeping session information.
3. an SSL wrapper: Pound will decrypt HTTPS requests from client browsers and pass them as plain HTTP to the back-end servers.
4. an HTTP/HTTPS sanitizer: Pound will verify requests for correctness and accept only well-formed ones.
5. a fail over-server: should a back-end server fail, Pound will take note of the fact and stop passing requests to it until it recovers.
6. a request redirector: requests may be distributed among servers according to the requested URL.

From Wikipedia:

Pound is a lightweight open source reverse proxy program suitable to be used as a web server load balancing solution... Using regular expression matching on the requested URLs, Pound can pass different kinds of requests to different backend server groups.

Pound home page.