I'm not sure where the most convenient connection is on an 89 (it's in the relay center on later models) but you certainly can bypass the neutral safety function of the NSS. Manual models just have an extra piece of wire that does essentially the same thing. Remember that the switch also sends shifter position information to the TCU and switches the backup lights, so you shouldn't actually remove or destroy it. But there's nothing to prevent you from finding the wire pair that goes to the NSS function, and putting a switch right across it. On 91-up models, there's a relay involved, and you can just use a little piece of wire in the relay socket.
The pertinent terminals on the connector are the bottom center pair, viewing the terminal with the retaining catch at the top. They should be numbered either 6 and 7 or B and C, I think. If you can identify the wires that apply to these, you should be able to trace them up to a convenient splicing point in the harness. I wouldn't splice down at the tranny end, owing to corrosion.
And of course, you need to remember that this is a neutral SAFETY switch, there to prevent runaway vehicles and lethal consequences, and I would strongly advise that if you feel the need to bypass it you do it with a switch that cannot easily be accidentally tripped, or if this is a hedge against future failure, perhaps just mark the wires for future jumping. And if you are already having trouble with the switch, do a search here for the relatively simple procedure for reconditioning it. Unless it's rusted onto the shaft of the transmission, it's an easy job.
