I wouldn't bother - Nippy Norman sells a nice set of risers which I've fitted on with my Renthal Twinwalls. Much much more comfy as my hands aren't at an odd angle any more.
Thanks Tobers for the advice, but that is the install that I'm riding with: Verholen risers with a ProTaper Henry/Reed. While I like the position, the bars are somewhat too far for me to reach comfortably. I'm looking to keep the rise that I have now (considerably lower than OEM) but closer.
I'm 5'6".
Henrique