(sorry, I wrote this post before I re-read and realized you wanted advice on a windscreen extension, not a recommendation on a windscreen)
I put a dark smoke zero gravity sport touring smoked windscreen on my 02 st4s - couple of inches taller than stock - doesn't get rid of all the wind but is a couple of inches taller than stock, looks good:
I'm 6 feet tall and it "softens" the wind that hits my head and shoulders. I'm sure some of the other riders on the site have other recommendations - I guess it's a matter of how concerned you are about looks and whether you want to reduce the wind or try to eliminate it as much as possible.
Thanks to both of you all...That's what I needed...I'am going to order the smoked Lip tonite and see if that helps...I'am short 5' 5" it should work...I had the tallest screen you could get for the 1098s and it worked great...Thanks Again Mike...