I preferred the old format as well, but as you noted, it's not easy to do with the (newer) "F3" format they've used in the past few seasons (they also didn't have a Sunday episode, where they could have covered a lot of the stuff they held for tonight).
You can't really have all F3 participate in the jury questions, because that would weigh too heavily on whoever wins Part 3 of the HoH's decision on _who_ to take with them to F2. There are other options though...
1. Extend the show to 2 hours... I've always felt that the Finale was too short anyway - I'd be happy to sit through more back-n-forth / recap from the HG (those who got to watch the season vs. those who hadn't seen it yet, etc.).
2. Do Part 3 ahead of time (not live on Finale night). There's no real reason to do that part Live - except for whatever amount of 'suspense' it leaves for Finale night (ie. live-feeders would already know ahead of time who the F2 were - but for that matter, they could just cut the feeds off for the last few days.. it's boring as hell by then anyway).
...I don't mind the format where the F3 hang in the house until Finale night, but I do miss the more in-depth jury questions they used to do.