I have had plans regarding this before, but wasn't entirely sure how to implement it.
I could add an option that lets you choose between -100% and +100% for instance, but I don't really see the value in this, as it would be a flat modifier.
The problem with acceleration is that it is variable, depending on how fast/slow you accelerate your mouse, so there's really no way to calculate this.
Any suggestion on what would work best?