This plugin would leverage the approaches used in http://drupal.org/sandbox/attiks/1319432 and/or http://drupal.org/sandbox/klausi/1320008, but wrap them in a PIFR plugin.

A new environment would be created for 'Project Applications', which would be limited to 'branch' tests; and only be triggered via a new PIFT trigger that would be implemented on either the project applications issue queue, or the sandbox project itself (if the owner doesn't have 'create full projects' access). This filtering may require the generation of a new 'test type' as well ... Suspect that more discussion needed on this front.