I've not grown them from seed, but I've grown Laurentia (Isotoma axillaris) plants here in the hot and steamy southeastern USA and it did great. When they got a little spent looking, I just cut them back really hard and fertilized. They would start blooming again within a few weeks. They didn't like to get over-watered. I lost them the year that we had non-stop rain and cool temperatures.
However, it sounds like you are trying to shift the seedlings from juvenile growth to flowering with vernalization, so I can't offer much help on that. I do have some old seeds that I might try so I'll be watching with you for any good advice.