Well, here's what a member over at GM-T.com had to say
"It has mostly to do with the switch stalk on the dash. There are some other GM vehicles of similar vintage that do have flash-to-pass switches on the steering colum that are of similar multi-function design (one that comes to mind off-hand would be the '96 Caddy Fleetwood).
I've known some folks to simply retrofit their vehicles using the stalk from a Fleetwood or other model with that functionality, and as far as I'm aware it should be plug-and-play. Just have to open up the steering column and replace the part. You might be able to find one NOS through a GM dealer, otherwise maybe hit up a salvage yard and see if you can find a GM multi-function stalk with flash-to-pass integrated"
Do you guys have any input on how to know if whatever switch I would buy would have this option?