For anyone coming here looking for the same solution, it should maybe be noted that the code Blake very helpfully posted will cause any onThrowEnd function you have to be called at the same time as onDragEnd as it sets the throw tween progress to 1 (ie finished so fire the onThrowEnd) and then back again.
I got round this by using 0.99 progress to do the hitTest, almost exactly the same as the final position, but without accidentally triggering my onThrowEnd before the throw has really begun
onDragEnd: function(){
var hit = false
if (this.tween) {
this.tween.progress(0.99)
hit = this.hitTest(centerpoint, '5%')
this.tween.progress(0)
}
},