I admit I was a little jealous of the new Vantage seats, particularly the articulated mesh lumbar support.
So, I tried one of these on my 2009 AI...

Oh my god, I have zero back soreness now. Maybe the best $5 I ever spent!
Got it
here on Amazon.
It stays on the seat without any problem (I just looped the strap behind the seat). At certain heights it will push against the support straps and loosen them, but I just move it up or down and the problem goes away. It pushes you forward a little as well but doesn't cause any issues for me.