My own scroller works. Now want to add 'click scrolling'

… and don’t know how to. What would be the best way to do it?

I want to be able to click in the area below/above the scroller mc to advance the scrolling in jumps (to a predetermined y-value or by x amount of pixels) but not past the max scrolling area either.

Here is the project as it stands, the top most link ‘capabilities’ shows the scrolling:

I haven’t been able to find anything online that helps me work this out.

My scroller works by taking the amount the scroller mc moves when you click and drag it, it takes the percentage moved and directs the text block to move according to this value. Here is the existing code that works:

var jgScrollUpper:Number = -3;
var jgScrollLower:Number= 496.5;
var jgTextLower:Number = 0;
var jgTextUpper:Number = -36.5;

var jgScrollRange:Number = jgScrollLower - jgScrollUpper;
var jgTextRange:Number = jgTextLower - jgTextUpper;

function jgScroll () {
    var jgMoved:Number = scroller_mc._y - jgScrollUpper;
    var pctjgMoved:Number = jgMoved/jgScrollRange;
    var jgtextMove:Number = pctjgMoved*jgTextRange;
    textBlock_mc._y = jgTextLower - jgtextMove;

scroller_mc.onPress = function  () {
    this.startDrag(false,this._x, jgScrollUpper, this._x, jgScrollLower); 
    this.onMouseMove = jgScroll;
scroller_mc.onRelease = Scroller_mc.onReleaseOutside = function  () {
    this.onMouseMove = null;

Any help most welcome,