I think Cobra had it pretty well. I just swapped my entire dash out about 3 times recently and I still can't remember the airbag mount completely and I had it on and off a half dozen times. If I remember, I'll take a picture of a dash chassis with the airbag sitting in it's location for you.
But.... the little crash computer that sits over your trans tunnel will get pissed off and throw an airbag light if you unplug that airbag.
IMO, the only way to do this right is to simply swap out the main dash plastic with a truck that has the switch (I have one in my truck right now) and swap the little crash box on the tunnel. Then the truck will do exactly what you want, and still be perfectly legal and operate as intended..... so that when the carseat is NOT in there.... the person riding with you can still have an airbag. Fwiw... you truck has the plug, as you've probably already seen if you've had the instruments out.
Otherwise..... you might just pin out the harness to the airbag and build a little "dongle" that replaces it. Body shops will HAVE these airbag impersonators just sitting around for testing purposes if a person was inclinded to find something like that...... just saying.....