Get a tape measure and throw it over head. And then try measuring shoulder-to-shoulder length. You can do whatever, but you shouldn't go significantly shorter. But remember once the bar is too short, you can't make it longer. (dah, I know) So you will be taking risks buying a riser that is already shortened. Also, note most of MTB handle grips are 120/135mm and some of those won't fit curves of risers.
Personally, I would avoid that bar for another reason. The dealer is deceiving you by stating wrong MSRP and appear to offer you discount which doesn't exist. I think you can buy that for 10-20 bucks without discount of any sorts.