I haven't played with the new HTML Form Builder Lite release enough to know if it does this, but I'm going to "assume" not (someone correct me if I'm wrong please) as I haven't heard any comments on this possible feature. I know many are hoping to see this in the Full version, but to be honest I don't know if they plan to add it or not.
In the meantime, if you are still using the Flash version of the Form Builder, you can easily create the fields you are talking about, they just won't be magical and show up by something that triggers them, they will just be always there. What I always do with fields that are sub fields is I indent them under the field they are connected to and I add a text box to the left in Caps and Red that says something to the order of:
If the above answer is YES, please fill in these 2 questions, if not please forward to the next section
You can word that however you like of course, but hopefully you get the idea. Just don't make them required fields so those that don't need to fill them in won't get stuck on your form and you should be good to go. Hope that helps and hopefully the feature you're asking about will make it into a future release of the new HTML Form Builder when it's published Full version. Check out this new version too it's pretty slick and when they get that one finished it's going to be sooooo awesome, it already is though so it's worth the upgrade for $29 as you get the new Web Image Studio a bunch of great images to use with it too!https://www.coffeecup.com/store/specials/megapack