Trail renderer algorithm?

Hey, I want to make a smoke line effect (like in CS:GO) and I was trying with the line renderer, but I can't figure out a good algorithm for this effect. I thought if I use the trail renderer and put some kind of constant force upward (like if the object was moving down, but it's position acctully is not changing) it would do the trick. But since you can't apply that "constant force", could someone give me a tip of the trail render algorithm, so i can reproduce it using the line renderer and make the effect? Thanks.