That's helpful but unfortunately doesn't work. The bzr repo isn't present by the time bootstrap is called. (I think it gets scrubbed before the actual build process, and probably before creating the source archive. The build itself happens in a separate process from the source package creation.)
As a last resort, one thing I can do is still use a recipe for the automated builds but instead of pointing the recipe at the auto-imported repo I could point to a launchpad repo that is "manually" sync'd to SVN trunk. (Where manual might be a cron job on one of my PCs)