Easier than I thought. Like your example I created a parent_holder mc with the registration point set to the centre. In this mc I place a child_holder mc with the registration point set to the top left.

After loading the jpg into the child_holder mc (make sure it's loaded) the width and height of both parent and child mcs is the same to that of the original picture. Let's say 150x150px.

So what I do is relocate the child_holder mc inside the parent_holder mc.

Code:
	if (_root.parent_holder.child_holder._x == 0 && _root.parent_holder.child_holder._y == 0) {
		_root.parent_holder.child_holder._x = (_root.parent_holder.child_holder._x-(_root.parent_holder.child_holder._width/2));
		_root.parent_holder.child_holder._y = (_root.parent_holder.child_holder._y-(_root.parent_holder.child_holder._height/2));
	}
In other words; if the loaded image is aligned to the registration point x0,y0 then align it so the centre of the image is right on top of the registration point. The centre of the image being half the width and half the height of the image. So move the image to x-75 and y-75.

Now if I rotate _root.parent_holder or zoom it or whatever... it will do so believing the centre of the image is the registration point

Hope this will help other folks out there as well... if you find a better solution let me know!

Cheers