wait the hard plastic or the vinyl part, i believe you're referring to the hard plastic right?
i've had a lot of import buddies who paint their interiors and they prep it by cleaning it and using paint thinner(i would use Paso, you can find it anywhere its a surface prep)
now my interior isn't painted i help ppl do it but thats about it and i just notice that the hard plastic tends to stick well when using prep, prime, paint and clear but i noticed no matter what the vinyl always seems to chip, even when we use the vinyl paint, not soon, it takes time for it to happen but eventually does.
but i don't know maybe its becasue we use stuff from o reily's and autozone, maybe if you find a better product is what i'm guessing
but it should work though, just try to find the best paint for that vinyl, you know where your arm rest is and right above it and i would think it should be ok