You still earn credits when you just Honk and leave, without opening the FSS. Those are "Level 1 scans". Since you can run the discovery scanner while scooping and while the FSD is charging up, if you start the Honk as soon as you arrive the Honk completes before the countsdown starts and you jump out of the system, so it shouldn't slow you down. It's free money once you sell the data - and free contributions to Exploration rating too, if you're not Elite yet.
I should point out that this is only true if you fire the Disco Scanner from a firegroup, rather than entering the FSS to fire it.