I've given this topic a bit of thought. I came to the conclusion that all we need is a little patience. Bees being bees, as soon as the population builds & there's a honey flow, the bees want to gather & store it somewhere for themselves or the next generation. The Flow frames, being plastic may not be ideal, but it will suit their purpose. It's just the nature of bees.
Another thing I pondered was the possibility of starting them off with a half depth super with starter strips. They are perfect for cut comb. Once the half depth super is full of sealed comb, remove it & replace it with the Flow frame super. That way you know that there is sufficient population to start on the Flow frames.
The cut comb out of the half frames certainly wont go astray & it will be easy to store the half box & frames after the comb is cut out & cleaned up.