Sous vide eggs - how to get a perfect soft-boiled egg?
Use fresher Grade AA eggs, this minimizes the amount of thin albumen. If this doesn't work you could perhaps try boiling it briefly when it's done cooking via sous-vide. I'd start with 60 seconds in boiling water, and going up from there to find the proper timing. I've never done this, but the boiling water should serve to quickly cook the runny whites.