I don't know if trimming off the flower stalks would encourage them to go back to normal growth, or if I'm just SOL with this batch of seedlings.
[Image description: a close up of a mulched garden bed with a bok choy seedling putting out a thin flower stalk.]
Too late to do anything once they've begun bolting. If you're expecting warm temps you can cover with ag fabric and spray it down, morning and afternoon, to keep temps underneath a bit lower, but that has to be done at the time/just before the heat sets in.