A picture of the part would be helpful. But, if you are referring to the Gilles Tooling Racing Lever and using it to switch to gp style, then I'm gonna say yes it will work. From what I can see and deduce, the Gilles lever allows you to switch to gp style by moving the shift rod connection to in front of the pivot point. So, you are still pushing when you upshift.
I could be wrong, but that is what it looks like to me. I believe that is how most, if not all, manufacturers make the rearsets so you can switch between standard and gp while still using the same QS.