I had the same problem, and resolved it by shortening the outer cable sheath. It is usually possible to remove the swaged on end, and re-use it.
I have found the best way to cut the sheath is with a cut-off wheel on a Dremel tool, being careful not to knick the inner cable.
In the end though, I am very happy with the new set-up. The 1/4 turn twist really makes the throttle response seem way better, even though technically you haven't changed it. Also, you don't have to re-position your grip to grab a handful of throttle in a hurry.