I believe I found a rather simple solution that will work for us: http://www.localwisdom.com/blog/2010/02/iis-7-reverse-proxy-share-1-ip-with-multiple-webservers/
Modules: ARR, URL rewriter
“For a very simple reverse proxy, all you have to do is:
Select the server node on inetmgr.
Double click on Application Request Routing icon.
Select/check “Enable proxy”.
Select/check “Use URL Rewrite to inspect incoming requests.
Enter the server of where you want to route the request to in “Reverse proxy” – ie. (myserver.contoso.com).
Our setup would be: www1, www2 - internal names for servers, these are referenced by separate IIS7 instance (responding to public IP and domain) which reverse proxies www1 or www2 as we please. ARR can be scripted too which would enable us to implement event-driven scenarios.