You could probably put a squirt of DT's in if you don't raise your own phyto.
When I used to grow Nannochloropsis and hatch brine, I would occasionally get my Nanno contaminated with a few baby brine, and they would grow to adulthood in the container. Just swimming and eating I suppose.
But you can also "gut load" the BBS by adding Selco or Selcon which is a nutritional additive. After the BBS hatch out they survive in the yolk sack for 12 hours. After that unless you feed them the have almost no nutritional value. So, you can hatch them out, change the water they are in and add Selco. Let them eat for a few hours or overnight, then change the water again and refridgerate.