In a lab setup, I want eth0 on a Ubuntu server box to get a DHCP address for talking to the outside world, and I also want to assign it a static 10.x.y.z address for talking to other boxes on the local network that have 10.x.y.z addresses. I want to do this by editing /etc/network/interfaces.

The man page for /etc/network/interfaces is modeled after "here's a bunch of examples, I hope you can figure out the actual rules on your own". I don't see a way to give one interface two addresses using two different methods (static and dhcp), and initial fumbling didn't produce useful results.