That's actually the exact purpose of the "Flatten Pages As Groups" setting. I've used it in the past and it works well.
The only caveat is that the tab order for form elements are then all the way down the first group and then starts again for the second group. To make this a little easier on the user, I create several pages (groups), and put related fields in each group. That way if the form is too long, the user is guided all the way down the page and then back up to the top.
You can see an example of this here and here.
Thanks for posting this as I think we forgot to post that the "Flatten Pages As Groups" option was added to FWP.