When I was doing the rope demo a few posts down I had to use the graphics.curveTo, but get it curve through a point instead of using the point as a control. I found a function a while back that I’ll try to source so I take no credit for it, but this is my revision of if.
Then you can use something like
var midPos:Point = new Point( 200, 200 );
var endPos:Point = new Point( 300, 300 );
midPos = curveThroughPoint( startPos, midPos, endPos );
this.graphics.lineStyle( 2,0x000000 );
this.graphics.moveTo( startPos.x, startPos.y );
this.graphics.curveTo( midPos.x, midPos.y, endPos.x, endPos.y );