Just spoke to dealer:
The device is a resistor so it means permanent disabling of the airbags. Basically this goes against either legal or insurance requirements so they (UK dealers) don't do it because a claim could be made against them in the case of a serious accident. If a key-switch is fitted, as many cars have these days, then turning off the airbag is down to the driver so there can be no legal claim against a dealer.
So, little ar, you'll have to stay in the back, even if Mummy's not with us .