Constraining startDrag() to trapezoid shape

programming flash
1

hei guys… how can i constrain the dragging of my movieClip inside the shape of a trapezoid?

here’s the code…

pamato.onPress = function() 
{
    startDrag(this, false, 1000, 270, 130, 605);
};


pamato.onRelease = function() 
{
    stopDrag();
    
    if(this.hitTest(_root.circle))
    {
        this._x = 620;
        this._y = 561;
    }
};

when i test the movie… its a rectangle… please help! thanks!