Watering little seeds in big pots?

This is a bit ghetto, but maybe if you have a handful of clay soil or something, you could put some of that around the seedling, water the pot thoroughly, cover whole pot with mulch. Either way, I'd probably recommend mulching if you need a bit of extra water retention.

I start all my seeds in their large "forever" pot. When it's just broken the surface I'll water gently right at the base of the plant. I give enough water to soak the soil down 10-12cm. Then a few days later I start watering 2 or 3 cm further out around the plant and start soaking the soil deeper. Providing moisture to encourage the new roots to grow outwards for the moisture. Then I just continue watering and ever larger area around the plant. It is important to remember that roots aren't going to grow out into bone dry soil. You need to be ahead of the growth with your watering and provide moisture for the roots to find. The end goal is to have your entire pot, top to bottom full of roots to support the biggest plant possible with the highest yield. It's also important to know that the root can be many times deeper than the plant above ground. That little sprout that's only 2 or 3 cm tall probably has a root down 10 cm looking for moisture and nutes.