I have, but not intentionally. Like Phat said, mostly it's been a case of persuading by example: they see that my load is lighter, mostly because I'm carrying less stuff; they ask why I don't have Widget X or Garment B, and we talk about it. Sometimes, next trip, they leave it behind, too. I remember one buddy who asked me how I liked my tarp-and-bivy setup (this was in the days before solo tents weighed the same as a tarp and bivy.) He asked, "But don't you miss having room to sort gear?" I answered, "Well, I really don't have much gear to sort..." Then we discussed his "sortable" gear: why he brought it, whether he needed it (not whether I needed it), and could he leave it behind next trip. Then we planned a trip where we looped back near the car on the second day, so he could start without it and pick it up later if he needed it. (Turned out he didn't.)

I've also helped a few folks go lighter, perhaps without them knowing it. As a recovering gearaholic (not too much "recovery" so far), I periodically pass lightly used gear along to others; frequently these are people new to backpacking who are trying to get a set of gear together. Because my choices are skewed toward lighter gear, their first setup is also going to be skewed that way; in turn, their methods and techniques will also tend to skew toward light when they add to, or replace, that initial set of gear.

It's never been an overt campaign as much as continuing evolution of our styles.