Occasionally I'll buy a few punnets of seedlings with the intention of planting them out, but for one reason or another, I get distracted from that task and I end up with a bunch of weak insipid looking seedlings that don't thrive when eventually planted out...here are a few tips for rescuing 'leggy' seedlings. Leggy Seedlings: What Causes Them and How to Fix Them - Garden Betty How to Fix Leggy Seedlings or The Art of Transplanting — Under A Tin Roof™
Have you tried any of these? I have a real problem with this because we get so little sun for so long (and not at all because I can't wait until the proper time to germinate because my fingers itch when I'm not planting...)