Ford can disable it for you, for peace of mind I would want it removed totally, I wouldn't trust an on / off switch fitted by a Ford monkey to guarantee the safety of my child. You might also need to inform insurance etc.

Personally I would leave your child in the back, if they require that much attention in the car when travelling on your own then I would make sure you carry another passenger. We left our daughter to her own devices in the car from a very early age, she now just pleases herself for hours when in her car seat!