If the truck has the two-stage airbags, it will have the afore-mentioned seat sensor. I'm not entirely sure that the Super Duties do (yet). I'd have to read a few more manuals to find out for sure...
Wish I had a solution for you... Short of moving up to a monster like a Kodiak or an F-650+, I'm not sure how you're going to be able to seat six and pull a trailer that heavy without having to deal with a passenger side airbag (and if a used Excursion is out of your price range, an F650 probably is too!)
But at the core of the issue, I don't think that deactivation is necessary for forward-facing occupants though, only rear-facing.
