Short of going in and removing the airbag itself, I don't think there is a way to disable it.
The reason that Ford didn't put the shut off switch in the SCREW is because Federal regs don't require it to be there. The reason it's there in a SCAB is because of 'kiddie safety' so that they 1) don't get their head taken off by an air bag and 2) carseats aren't pushed back towards the seat causing infant damage.
With a screw, you have to put the kiddies in the rear seat. It's just like an Expedition, Suburban, Blazer, Explorer etc... they don't have shut offs either... and never will until the federal government requires them to do so...
*note, if you're going to toy with the airbag, I HIGHLY RECOMMEND that you disconnect the battery prior to tinkering. Those things ignite with a type of 'weak blasting cap'. They can definately take off a finger and ruin your day.