Virtual Hosting With mod_proxy

The other day I had someone ask if there’s a nice solution to the following problem: Multiple web development virtual machines but only one external IP address. The quick solution is to port forward on different ports to each virtual machine. For example 81 goes to VM1, 82 goes to VM2, 83 goes to VM3 etc. Which granted, would work, but isn’t a “neat” solution. Using mod_proxy under Apache is