Drive two hours: no.
Fly a different day: maybe...
Seattle a day early, in the summertime?
YES - excellent call, Seattle rocks in the summer. Lots of stuff there that kids will dig, too. ^
If flying a day early wasn't really feasible, all hope is not lost:
(1) Check the website often - you might just randomly get lucky and someone has canceled, upgraded, or changed seats from the back of the plane into an elite-only seat.
(2) Figure out exactly when that airline's elite upgrades process. That might free up some seats in coach. Granted, some of these free seats might come out of the elite-only area that you can't see but all you need is one or two non-middles to shake free.
(3) At the airport, the system may open up more seats for assignment. If you check in early you might have a better chance of getting a non-middle or two.
(4) If the airline offers any kind of "elite for a day" option, maybe buy a couple seats with this. Especially if you intend to check two or four total bags...sometimes it's not a bad deal, especially if it frees up one of those front-aisle or front-window seats.