Have you tried lptools?

It’s not at all officially associated with the Launchpad project, of course, but it’s got a few nice things that you might want to look at, including:

a milestone manipulator
a code review notifier, and
a milestone to iCal exporter

One of these days, I’d like for there to be an official, awesome Launchpad command-line client. As it is, I’m happy with the world of people making extensions to meet their needs.

For other extensions, check out the lpx project or our list of clients.