You don't, not really

.
You'd need to make that an actual upstart job and listen for the framework_started event, and/or add another job that does something you can react to based on that event.
Fair warning: if you break upstart, or just subtly break the dep chain, you break the boot. Which potentially means a softbrick because of the failed startup counters. (e.g., have the RP/CRP at the ready if supported by your device, or have serial access otherwise. Barring that, big brassy balls required).