As long as you are aggressively feeding/watering an auto, you could get by with some rapid successive uppotting, but as shruum suggested, you are on a time clock with an auto... and she is going to do what she wants to do, despite you concentrating on roots. There just isn't time with an auto to build a massive rootball... she builds what she needs and then moves on to building buds. I used to be in the camp that a plant is a plant is a plant, and that there was no reason to not use the successive uppotting strategy even with an auto, but after trying it a few times and seeing how anemic the root growth was and how impossible it was to get a solid rootball developed before flowering started automatically, I have changed my mind on this. I now see little use of going much larger than a 3 or 5 gallon for auto plants, and I would do exactly as you are doing now... get them a good start in a smaller container and then transplant them to the final container and call it good.